Formed Thermoplastic Article Having a Peelable Surface and Smooth Edges

ABSTRACT

The disclosure relates to forming shaped thermoplastic articles having smooth peripheries. Many thermoplastic articles have sharp edges formed upon molding or cutting the article from a feedstock sheet. Such sharp edges can damage thin plastic films or flesh which they contact, and smoothing the edges is desirable. Described herein are methods of forming a smooth periphery for such sharp-edged articles by rolling over the sharp edge. The smoothing operation is performed by forming a deflectable flange including a bend region separated from the potentially sharp peripheral edge by a spacer, deflecting a portion of the deflectable flange, and softening at least one bent portion of the deflectable flange to yield a smooth periphery upon cooling. A liner sheet may be attached to the feedstock sheet prior to, during, or after forming and can be peelable therefrom.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S.non-provisional patent application Ser. No. 15/445,220, filed 28 Feb.2017, which is a continuation-in-part of co-pending internationalapplication PCT/US16/49692, filed 31 Aug. 2016, which is entitled topriority to U.S. provisional patent application No. 62/212,367, filed 31Aug. 2015, each of which applications is incorporated herein byreference in its entirety.

BACKGROUND OF THE DISCLOSURE

This disclosure relates generally to the field of forming shapedthermoplastic articles.

Formation of shaped articles from thermoplastic materials is well known.A wide variety of methods (e.g., thermoforming, casting, molding, andspinning) can be used to confer shape to a molten thermoplastic or to apreformed thermoplastic sheet that has been softened or melted.

Trimming of waste material from one or more edges of a shaped article isa common finishing technique, but leaves a sharp edge that can injureflesh or tear or cut materials which come into contact with the edge.One common use for shaped thermoplastics is to form containers that canbe sealed with thin plastic films, such as trays, bowls, or binsintended to contain foodstuffs and intended to be sealed withtransparent plastic film. Another common use is to contain items and toseal them from moisture or other materials which may come into contactwith the container. Sealing of such containers typically involvesextending or stretching the film across a compartment formed in thecontainer and sealing the film around the periphery of the compartment,which periphery is often situated adjacent a trimmed edge of the articlethat includes the compartment. If that edge is sharp, it can cut orbreak the film, interfering with the sealing process.

Three well-known sealing technologies are commonly used in sealing foodsand foodstuffs to form containers for commercial shipping, storage,display, and sale. These are referred to herein as OW, VSP, and MAPtechnologies. All of these technologies involve combining a containerand a thin plastic film. Owing to the fragility of such films and theneed, in many instances, to minimize or eliminate punctures and tearsfrom film portions which serve to define (together with the container)sealed compartments, it is critical to minimize the opportunities forcontainers to tear, puncture, or abrade the film of the same or nearbycontainers. In addition to plastic films used for sealing suchcontainers, plastic films are also employed for shipping the containers,such as the “mother bags” (i.e., typically thin plastic bags) used forcontaining multiple product-in-container-packages during shipping andthe plastic grocery bags used by consumers to transport purchased goodsfrom a retailer. This can be achieved by reducing or eliminating sharpor rough container edges, at least positions on the container at whichsuch edges might reasonably contact the film during packaging, storage,shipment, or display.

Overwrap (OW) technology involves enveloping or wrapping a shapedarticle (e.g., a thermoformed tray, sheet, bowl, or multi-compartmentcontainer) with a thin (often transparent) plastic film after afoodstuff or other item has been placed on one or more faces of thearticle and thereafter sealing the film to itself (e.g., by heatingoverlapping portions of the film). In such OW technology, sharp or roughedges of the shaped article can cut, abrade, or puncture the film,potentially allowing materials to pass through the film and defeatingone or more of its purposes. Heretofore, OW technology has been usedprimarily together with foamed trays or bins lacking sharp edges. Manymunicipal recycling schemes exclude or disfavor foamed plastics, andsuch materials are therefore increasingly disfavored by consumers. Itwould be desirable if a thermoformable plastic container suitable foruse with multiple wrapping technologies, including OW technology, couldbe made, since thermoformable materials tend to be widely acceptable inrecycling programs.

Vacuum-sealed package (VSP) technology involves adhering a thin (again,often transparent) plastic film against a face of a shaped articlebearing a foodstuff (for example, or a moisture-sensitive object as analternate example) on a face of the shaped article. When VSP technologyis employed, that item(s) to be packaged are placed on a surface orwithin a cavity of the shaped article, the film is overlain such thatthe item(s) are interposed between the shaped article and the film, air(or whatever other gases may be present) is withdrawn from the spacebetween the film and the shaped article (optionally in coordination ofapplication of positive pressure to the exterior of one or both of thefilm and the shaped article) so that the film is closely opposed againstthe surface of the shaped article and/or the item(s), and the film issealed (e.g., by way of an interposed adhesive, through heat-inducedadhesion, or by static charge adhesion) to the surface of the shapedarticle across the desired area (usually completely encircling theitem(s)), and any excess film can be trimmed from the desired area. Theseal can be resistant to gas flow in order to maintain the gas-evacuatedstate on the interior of the sealed container. The resulting VSP-sealedpackage typically has a topology that mimics the shape of the surface ofthe shaped article having the item(s) thereon.

MAP is an abbreviation for modified atmosphere packaging and refers to asealing technology in which a flexible (often transparent) film issealed (e.g., using heat or an adhesive) about the perimeter of asubstantially rigid shaped article. When the shaped article is otherwiseclosed (i.e., when it has no other openings than that sealed by thefilm), the gases present within the container can be controlled at thetime the film is sealed to the article. Thus, if the article and filmare sealed in the presence of a selected atmosphere (e.g., a gas, suchas one selected to exclude oxygen or to promote fruit ripening), theselected atmosphere can be maintained within the sealed MAP packageduring subsequent storage, shipping, and display of the package.

As is known in the art, the shaped articles used in OW, VSP, and MAPsealing processes tend to have a variety of industry-accepted geometricshapes and properties which differ among the three types, such that ashaped article useful in one type of sealing process is often poorlysuited for use in one or both of the others.

Containers used for OW-sealing, for example, tend to be rectangular andtray- or sheet-shaped, with smooth, blunt edges and rounded corners. Thelack of sharp, rough, or pointed edges or corners serves to reduce thelikelihood that the film used for overwrapping the container will betorn or punctured upon wrapping. OW-containers often have a flat portion(e.g., on the “bottom” of the container, relative to its intendeddisplay configuration) at which the overwrapped film can be urgedagainst itself for the purpose of sealing the film to itself (e.g., uponapplication of heat to the overlapping film portions sufficient to causesuch sealing), thus enclosing the container and any items on or in it.

Containers used for VSP-sealing tend to have a face or surface(sometimes within a concavity) adapted to carry an item to be sealedbetween the film and the container and adapted to receive the sealingfilm by virtue of the absence of sharp points, protrusions, or edges.The absence of such features reduces the likelihood of punctures ortears in the film as it is drawn against the surface. UnlikeOW-containers, VSP-containers can have sharp edges, corners, orprotrusions, at least at portions other than the film-receiving surface,because those portions need not contact the film during sealing.However, such sharp portions can still damage sealing films, especiallywhen multiple VSP-sealed packages are stored, shipped, or displayed nearone another, because a sharp portion of one container can damage thefilm of another container (or a film or tissue in the vicinity of thecontainer).

Containers used for MAP-sealing tend to have a planar surface (e.g., abroad, flat rim) surrounding an opening to be sealed by applying a sheetof film against it, sealing the film to the surface (often substantiallyirreversibly), and then trimming the film about the perimeter of theseal. Such containers must be configured such that the film can beapplied to the surface without substantial risk of tears or puncturesbefore and during sealing and to facilitate trimming of the film fromthe sealed container. However, because the film typically contacts onlylimited portions of MAP-containers during the sealing process,MAP-containers can, and often do, include sharp, pointed, or abrasivefeatures at positions not involved in the sealing process.

It would be beneficial if the sharp edges of shaped thermoplasticarticles could be displaced in such a way that the risk of injury ordamage to sealing films could be reduced. It would be further beneficialif such individual shaped articles could be used with multiple knownsealing technologies, such as two or more of OW, VSP, and MAPtechnologies. Reducing the sharpness and tendency of thermoformedarticles to induce damage and injuries would be advantageous even in theabsence of sealing. The subject matter disclosed herein addresses thisshortcoming of prior shaped thermoplastic articles.

Others have recognized the desirability of reducing the occurrence ofsharp edges at the edges of trays to be overwrapped. For example, Nelsonet al. (U.S. patent application publication number 2015/0001127)disclosed a packaging tray that is formed by thermoforming a film sheetto yield a precursor tray having a generally U-shaped flange about itsperiphery, the open end of the U facing the sealing surface and theperipheral edge of the tray jutting peripherally. Nelson's tray is madeby cutting the precursor tray from a sheet of thermoformable material toyield an end in which the peripherally-extending peripheral edge ispositioned at the terminus of the outer (relative to the tray body) armof the U. Nelson then compresses that outer arm inwardly toward the traybody, leaving a smoother crimped portion of the U-shaped flange at theperiphery of the tray, with the still-potentially-sharp peripheral edgeextending toward the sealing surface. In this way, Nelson et al.,generates a tray said to be suitable for overwrapping, an overwrappingfilm being intended to urge the outer arm of the U-shaped flange towardor against the inner arm. However, because the tray retains a sharpperipheral edge in a position in which it can cut films (the peripheraledge of Nelson's trays can be seen to contact both the film overwrap andthe film overwrapping an adjacent tray in Nelson's FIG. 13A, forexample), Nelson's tray remains unsuitable for all OW applications andgenerally unsuitable for use with VSP and MAP technologies. A traylacking a film-accessible sharp peripheral edge or a sharp crimps (whichNelson's trays also possess—see item 124 in Nelson's FIG. 12A) would bepreferable for use with each of these sealing technologies.

The subject matter disclosed herein includes shaped thermoformedarticles which are suitable for sealing with multiple technologies.

Thermoformed drinking cups having smooth, rolled edges are also known.Such cups are made by thermoforming cups having a flange about theperimeter of the cup opening, the flange including a potentially sharpperipheral edge at the flange end distal to the interior of the cup. Theflanged cups are stacked in a nested fashion, heated at their flangeportions, and then passed through helical rim-rolling threads to createthe rolled edge. Such technology is useful only for rolling the edgesurrounding a circular orifice, and is therefore of no practical use inmaking shaped articles having rolled edges surrounding non-circularopenings. Rolled-edge drinking cups are also not designed to facilitatewrapping or sealing with thin plastic films.

BRIEF SUMMARY OF THE DISCLOSURE

The disclosure relates to methods of displacing a sharp edge away fromthe periphery of an article made from a thermoplastic material, wherethe sharp edge might otherwise damage surfaces that contact theperiphery of the article. The disclosure also relates to articlesprocessed according to those methods and to equipment for performingsuch processing.

The disclosure relates to a method of forming a smooth edge (i.e., asmooth periphery) on an article made of a thermoplastic material. Themethod includes a step of forming a deflectable flange at an edge of thebody of the article. The deflectable flange includes a peripheral edgeof the thermoplastic material at the peripheral end of the deflectableflange, optionally on a peripheral flange that extends peripherally fromthe deflectable flange. In one embodiment, the peripheral flange isconnected by an elbow to a spacer and extends peripherally beyond thespacer by a peripheral flange distance. The peripheral flange distancecan be selected to yield a desired degree of deflection when it isimpinged against a surface. In one embodiment, the peripheral flangedistance is selected to be zero (i.e., the peripheral edge exists wherethe elbow would otherwise be. The spacer is connected by a bend regionto the body, the bend region defining an angle (which can be acute orobtuse, and is preferably approximately a right angle) between thespacer and the body. The deflectable flange is urged within the interiorof a cavity defined by an upper body, for example, the distance betweenthe elbow and the interior being smaller than the peripheral flangedistance, so that the deflectable flange is deflected at the bend regionupon impingement of a portion of the interior of the cavity on theperipheral flange. Sufficient heat is applied to the bent portion (here,the bend region) of the deflectable flange to soften the thermoplasticmaterial at the bend region. The upper body and the article areseparated, whereby the bend region remains deflected upon cooling,yielding a smooth edge (i.e., periphery) on the article.

This method can be used to form a smooth edge about the entire peripheryof the article. To do so, the deflectable flange is formed about alledges of the article and the interior of the cavity is configured tosimultaneously impinge upon the deflectable flange about all edges ofthe article when the deflectable flange is urged within the interior. Inthe resulting article, the peripheral edge is effectively ‘hidden’(e.g., it is behind the deflected peripheral flange or deflected awayfrom the periphery of the article) so that materials (e.g., thin plasticfilms or animal tissue) which contact the periphery of the article willbe less likely to contact the peripheral edge of the thermoplasticmaterial from which the article is made.

The disclosure also relates to a method of forming a sealed compartment.This method includes steps thermoforming a thermoplastic sheet to forman article having a concave compartment surrounded by substantiallyplanar sealing surface, cutting the article from the sheet peripherallyto the sealing surface, forming a smooth edge about the entire peripheryof the article as described herein, and thereafter sealing a top sheetto the sealing surface to form the sealed compartment. In one embodimentof this method, the top sheet is trimmed peripherally about the sealingsurface after it is sealed to the sealing surface. In anotherembodiment, the top sheet is heat-sealed to the sealing surface.

The disclosure further relates to a method of forming a sealedcompartment. This method includes steps of thermoforming a thermoplasticsheet to form an article having a concave compartment surrounded bysubstantially planar sealing surface, cutting the article from the sheetperipherally to the sealing surface, forming a smooth edge about theentire periphery of the article as described above, and thereafterwrapping and sealing a flexible plastic film about the article to formthe sealed compartment.

In some embodiments of the methods described herein, after urging thedeflectable flange within the interior of the cavity and beforeseparating the upper body and the article, a ram can be urged into theinterior, closely opposed against the interior, behind the deflectableflange to an extent that a face of the ram impinges upon and furtherdeflects the deflectable flange, for example, at the bend region. Theface can be substantially planar, for example. The face can also besubstantially perpendicular to the portion of the interior that impingesupon the peripheral flange. The face can define an obtuse angle with theportion of the interior that impinges upon the peripheral flange. Theface can have a concave profile, relative to the interior. If the ram isheated, urging the ram against the deflectable flange can cause bendingof the portions of the deflectable flange which contact the ram, furtherdeflecting the peripheral edge of the thermoplastic sheet away from theperiphery of the shaped article.

In a non-heat-based embodiment, the disclosure relates to a method offorming a smooth edge on an article made of a plastic material (e.g., athin plastic material backed by a deformable metal layer). This methodincludes forming a deflectable flange at an edge of the body, thedeflectable flange including a peripheral edge of the thermoplasticmaterial at the peripheral end of a peripheral flange. In oneembodiment, the peripheral flange is connected by an elbow to a spacerand extends peripherally beyond the spacer by a peripheral flangedistance (which is effectively zero if there is no peripheral flange).The spacer is connected by the bend region to the body or an extensiontherefrom. The bend region defines an angle (which can be acute orobtuse, and is preferably approximately a right or slightly obtuseangle) between the spacer and the body. The deflectable flange can urgedwithin the interior of a cavity defined by an upper body, the distancebetween the spacer and the interior being smaller than the peripheralflange distance or impinged upon a shaped ram surface that deflects thedeflectable flange inwardly. The deflectable flange is therebydeflected, such as at the bend region, upon impingement. Sufficientpressure is applied to irreversibly bend the plastic material. The upperbody and the article are separated, whereby the deflectable flangeremains deflected upon removal of pressure, yielding a smooth edge onthe article.

BRIEF SUMMARY OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 consists of FIGS. 1A, 1B, and 1C and illustrates the basicoperation of the structures and methods described herein. Parallelstraight lines “//” indicate positions at which structures, dimensions,and proportions which can optionally be present are omitted for clarity.

FIG. 1A illustrates a sectional view of a thermoplastic article 100having a deflectable flange 160 formed at an edge thereof. Thedeflectable flange 160 in this embodiment includes an extension 50, abend region 150, a spacer 140, and a peripheral flange 120. Theextension 50 connects the shaped body 10 of the article 100 to the bendregion 150 of the deflectable flange 160. A spacer 140 can be (andpreferably is) interposed between the bend region 150 and the peripheralflange 120. The peripheral flange 120 is connected to the spacer 140 byway of an elbow 130, which is shown as a right-angle bend in thisembodiment. The bend region 150 connects the extension 50 and the spacer140 at an approximately right angle (the angle designated A). Theperipheral flange 120 terminates at the peripheral edge 110 of thethermoplastic material (represented by a thick solid line in thisfigure) of which the article 100 is formed.

FIG. 1B illustrates the thermoplastic article 100 inserted within theinterior of an upper body 200, which is shown as a broken-away portion(indicated by the rough line). In this embodiment, impingement of theperipheral edge 110 of peripheral flange 120 upon the inner surface 202of the upper body 200 causes the deflectable flange 160 to defect, owingto bending of the deflectable flange 160 at one or more points B withinthe bend region 150.

FIG. 1C illustrates the outcome of inserting ram 300 (only a broken-awayportion shown, as indicated by the rough line) into the interior of theupper body 200 behind the thermoplastic article 100 (i.e., when the ram300 is inserted into the structures illustrated in FIG. 1B). The ram 300is closely opposed against the inner surface 202 of the upper body 200and the the peripheral edge 110 of peripheral flange 120 impinges uponthe upper face 302 of the ram 300, causing even greater deflection ofthe deflectable flange 160 and yielding a rounded periphery to article100 at the point(s) B at which bending is induced within the bend region150.

FIG. 2 consists of FIGS. 2A, 2B, 2C, and 2D and illustrates a matchedupper body 200 and ram 300 for deflecting one or more deflectableflanges 160 formed on the periphery of a shaped thermoplastic articlehaving the conformation of a rectangular tray with rounded corners. FIG.2A illustrates the upper body 200 disposed above the ram 300, and FIG.2B illustrates the upper body 200 engaged with the ram 300. FIG. 2C is acutaway view of the engaged upper body 200 and ram 300 shown in FIG. 2Band illustrates that a portion of the ram 300 fits within and closelyopposed to the interior surface of a recess in the upper body 200. FIG.2D is a detail of the section indicated in FIG. 2C and illustrates theclose opposition between the ram 300 and the interior of the upper body200. In FIG. 2D, the sloping conformation of the upper face 302 of theram 300 is apparent.

FIG. 3 consists of FIGS. 3A, 3B, and 3C, which are images of a smoothedperiphery and corner of a clear, shaped thermoplastic article having theconformation of a rectangular tray with rounded corners. The article wassmoothed using an upper body 200 and ram 300 similar to thoseillustrated in FIG. 2. In FIG. 3A, a finger is visible within theinterior of the tray, and the smoothed corner is visible to the left ofthe finger. Also visible at the portion where the finger is located is astacking lug, which is a portion of the corner of the tray which extendsperipherally to a greater extent than the portion of the corner belowthe finger. Extending (downwardly in the figure) from the smoothedcorner is a smoothed straight sidewall of the tray. Wrinkling of theperipheral flange is visible beneath the smoothed corner, and deflectionof the peripheral flange under the smoothed straight edge can be seenbehind the corner on the left side of the figure. FIG. 3B is anotherview of a smoothed corner of a similarly-made tray, also seen from belowthe rim of the tray. The prominent extension at the corner just belowthe rim is a stacking lug. FIG. 3C is a view of the smoothed corner,with a finger pointing to a smooth region formed by bending, softening,bending, and cooling of the bend region of the deflectable flange. Thissmooth region can, for example, be urged against a thin plastic filmwithout tearing it easily, since the relatively sharp edge of thethermoplastic material from which the tray is formed is bent under thecorner, as shown in FIGS. 3A and 3B.

FIG. 4 illustrates a section taken through a storage container article100 being formed using the methods described herein (parallel straightlines “II” indicate positions at which structures, dimensions, andproportions which can optionally be present are omitted for clarity). Inthe figure, the article 100 has a deflectable flange 160 formed on eachof the sides of the container visible in the figure. A single upper body200 extends across the entire container, including around the sides atwhich the deflectable flanges 160 are located. A single ram 300 (onlytwo portions shown in the figure) has been inserted within the interiorof the cavity in the upper body 200 behind the article 100. Theperipheral edge 110 of the thermoplastic sheet from which article 100 isformed, infringes upon the upper face 302 of the ram 300 at eachdeflectable flange 160, causing the deflectable flange 160 to deflectinwardly toward the body of the article 100 by flexing at one or moreportions B of the bend region 150 of each deflectable flange 160.Application of heat at B in an amount sufficient to soften thethermoplastic sheet causes the deflectable flanges 160 to retainapproximately the conformation shown in this figure, with the peripheraledges 110 of the thermoplastic sheet positioned anti-peripherally (i.e.,within the periphery of the article 100, which occurs at the positionsindicated by B in this figure), yielding smooth peripheries to theformed container upon cooling of the softened portions.

FIG. 5 consists of FIGS. 5A, 5B, and 5C, each of which illustrates asection taken through a storage container article 100 being formed usingthe methods described herein (parallel straight lines “//” indicatepositions at which structures, dimensions, and proportions which canoptionally be present are omitted for clarity). In the figure, thearticle 100 has a deflectable flange 160 formed on each of the sides ofthe container visible in the figure. The deflectable flanges 160 havebeen deflected inwardly by infringement thereupon by the upper face 302of a single ram 300 (only two portions shown in the figure) at eachdeflectable flange 160. The peripheral edge 110 of the thermoplasticsheet from which article 100 is formed, infringes upon the upper face302 of the ram 300 at each deflectable flange 160, causing thedeflectable flange 160 to deflect inwardly toward the body of thearticle 100 by flexing at one or more portions B of the bend region 150of each deflectable flange 160. Application of heat at B in an amountsufficient to soften the thermoplastic sheet causes the deflectableflanges 160 to retain approximately the conformation shown in thisfigure, with the peripheral edges 110 of the thermoplastic sheetpositioned anti-peripherally (i.e., within the periphery of the article100, which occurs at the positions indicated by B in this figure),yielding smooth peripheries to the formed container upon cooling of thesoftened portions. In this embodiment, the two parts of the ram 300 areshown with different profiles (one flat and one curved), to illustratedifferences in deflection that can be induced by the different profiles.FIGS. 5A, 5B, and 5C differ in the distance between the elbow and theperipheral edge, this distance being greater in FIG. 5A than in FIG. 5Band being zero in FIG. 5C.

FIGS. 6A, 6B, 6C, 6D, and 6E illustrate deflectable flanges formed intray-shaped articles thermoformed from a sheet of thermoplasticmaterial. In each of FIGS. 6A and 6B, a finger touches the sharp edge(i.e., the peripheral edge 110 at the periphery of peripheral flange120) where the tray has been cut from the sheet. In these figures, thedeflectable flange has not yet been softened, deflected, and cooled, sothe sharp edge remains positioned about the periphery of the tray. Bycomparison, the sharp edge has been deflected inwardly and away from theperiphery of the trays shown in FIG. 3 and in the tray shown in thelower portion of FIG. 6C. The tray shown in the upper portion of FIG. 6Cis the same as that shown in the lower portion, differing in that thetray in the upper portion has not had its deflectable flange “rolledover” as the tray in the lower portion has. FIG. 6D is a view from theunderside of a rounded rectangular tray which has a “rolled over” edgeabout its entire periphery. The absence of sharp edges at or near theperiphery of this tray is visible. FIG. 6E is an oblique view of threeinitially-identical trays, each having a “rolled over” edge as describedherein, the degree to which the edge has been “rolled over” differingamong the three. The tray labeled “1” has a peripheral edge that hasonly barely been “rolled over” (i.e., the portion of the deflectableflange including the peripheral edge 110 has been deflected not morethan about 45 degrees inwardly from the plane of the remainder of thespacer 140, most which remains substantially flat in this tray. The traylabeled “2” has a peripheral edge that has been more fully “rolledover”—so much so that the peripheral edge 110 can nearly not be seen (ithas been ‘tucked’ behind the remaining visible portion of the spacer140). On the tray labeled “3,” the deflectable flange has been rolledover further still and the peripheral edge 110 cannot be seen. That thedeflectable flange of tray “3” has been rolled over to a greater degreethan that of tray “2” is detectable by virtue of the shorter portion ofspacer 140 that remains visible on tray “3” than on tray “2” (and thevisible portion of spacer 140 of each of trays “2” and “3” is shorterthan the visible portion of spacer 140 of tray “1.”) The three traysshown in FIG. 6E can thus be thought to illustrate discrete degrees of“rolling over” of the deflectable flange.

FIG. 7 consists of FIGS. 7A, 7B, and 7C and illustrate an embodiment inwhich an article 100 formed of a thermoplastic sheet (parallel straightlines “II” indicate positions at which structures, dimensions, andproportions which can optionally be present are omitted for clarity)resting on a horizontal surface (solid horizontal line) has itsperipheral edges smoothed as described herein. In this embodiment, anupper body 200 (two portions shown in this cross section) is loweredover the article 100 in the direction indicated by the open arrow,causing each of the article's two deflectable flanges 160 to deflectinwardly. In FIG. 7A, outwardly-flared portions of the upper body 200have just contacted the peripheral flanges 120 of the article 100 as theupper body 200 is lowered onto the article toward the horizontalsurface; the deflectable flanges are beginning to deflect at the areasmarked “B.” In FIG. 7B, the the upper body 200 has been lowered onto thehorizontal surface, and the peripheral edges 110 and the peripheralflanges 120 of the article 100 are partially deflected inwardly towardthe body 10 of the article 100. In FIG. 7C, the ram 300 has beeninserted, in the direction indicated by the open arrow, into a cavity inthe upper body 200 behind the article 100 and further deflects theperipheral flanges 120 (and, with them, the deflectable flanges 160)through bending of the thermoplastic sheet of which the article isformed at the areas marked “B.”

FIG. 8 consists of FIGS. 8A, 8B, 8C, 8D, 8Di, 8Dii, 8E, 8F, 8G, 8H, 8J,and 8K and illustrates deflection and rolling over of the deflectableflange 160, including the sharp peripheral edge 110 thereof using a ram300 as described herein. Each of FIGS. 8A-8C, 8E-8G, and 8H-8K is across-sectional view including only one edge of the article; the samedeflection and rolling over of the edge can be performed on multipleedges (e.g., all edges) of the article simply by using multiple rams ora ram that contacts all edges to be so treated.

FIGS. 8A, 8B, and 8C sequentially depict the effect of urging the shapedarticle 100 farther against the ram 300 in the direction indicated bythe open arrow in each figure, as can be seen by comparing the portionof the article appearing in the left portion of each figure. In theembodiment shown in FIGS. 8A-8C, the deflectable flange 160 lacks anelbow and a peripheral flange. The initial (pre-ram-impingement)conformation of the shaped article is that shown in FIG. 9A.

In FIG. 8A, the article has been urged against the ram such that itsdeflectable flange 160 contacts the upper face 302 of the ram at itsperipheral edge. The deflectable flange 160 deflects from itspre-contact position by virtue of resistance to movement encountered bythe deflectable flange as it contacts the inclined portion of the upperface 302. In the figure, the peripheral edge 110 of the deflectableflange rests against the upper face at a position where the inclinedportion of the upper face transitions to a curved contour and a portionof the spacer is in close proximity to the ram, which is heated andtransfers heat thereto.

FIG. 8B shows the effect of urging the article 100 depicted in FIG. 8Afurther against the ram 300. Because the ram 300 shown in FIG. 8B isheated, it softens the material from which the deflectable flange 160 ismade at portions where the deflectable flange is in close proximity toor contacts the upper face 302 of the heated ram 300. Because of theshape of the upper face 302, the deflectable flange 160 reaches aposition at which it can no longer advance by merely sliding along theupper face surface. Because the article 100 (including the deflectableflange 160) is being urged in the direction indicated by the open arrow,and because the material of which the deflectable flange is constructedhas been softened by the heated ram 300, the deflectable flange deforms(at positions B) to follow the contour of the upper face 302 of the ramas the deflectable flange is advanced against the ram.

FIG. 8C shows the effect of continuing to urge the article 100 depictedin FIG. 8B against the heated ram 300. As the article (including thedeflectable flange 160) is urged in the direction indicated by the openarrow, the deflectable flange continues to bend where softened bycontact with the heated ram (i.e., at positions B). As movement of thedeflectable flange against the ram continues, the peripheral edge 110 ofthe deflectable flange eventually reaches an edge of the upper face 302of the ram. The portion of the deflectable flange including theperipheral edge remains softened for a period of time (the period beingdependent on the operating conditions in predictable ways). If theperipheral end contacts a portion of the article 100 while softened, itcan be deflected thereby (e.g., upwardly, as suggested in the embodimentshown in FIG. 8C). Deflection of the portion of the peripheral flangeleaving contact with the upper face can also be influenced by thecontour of the upper face 302, for example inducing a “curled” or“spiraling” conformation as shown in FIG. 8C.

FIG. 8D illustrates using one or more objects to assist with deflectionand rolling over of the deflectable flange as describe herein. Object401 (referred to elsewhere herein as a plug) is disposed within aninterior compartment of the shaped article 100 and abuts against aninner surface of the shaped article 100 during impingement of thedeflectable flange 160 against the ram 300, in order to reduce orprevent inward deflection of the inner surface during the operation.Object 403 applies downward pressure (open arrow) against, in thisembodiment, the extension 50 portion of the deflectable flange 160, inorder to impinge the deflectable flange 160 against the upper surface302 of the ram 300. In this embodiment, object 402 rigidly connectsobjects 401 and 403. Filled arrows depict forces imposed upon thearticle 100 upon application of the downward pressure. FIG. 8Di depictsa shaped article in the form of a rounded rectangular tray T having aninterior and a plug P that is shaped and dimensioned to fit within thatinterior, so as to act as object 401 in FIG. 8D and to reduce or preventinward deflection of the side walls of the tray T during the rollingover of the deflectable flange of the tray T. FIG. 8Dii shows the pluginserted within the interior of the tray.

FIGS. 8E, 8F, and 8G (analogously to FIGS. 8A, 8B, and 8C) sequentiallydepict the effect of urging the shaped article 100 farther against theram 300 in the direction indicated by the open arrow in each figure. Inthe embodiment shown in FIGS. 8E-8G, the deflectable flange 160 includesa peripheral flange 120 at the peripheral end of the spacer 140. In thisfigure, it can be seen the peripheral flange 120 deflects during bendingof the deflectable flange 160 to the extent that it becomesindistinguishable from the spacer 140.

FIGS. 8H, 8J, and 8K (analogously to FIGS. 8A, 8B, and 8C; FIG. 8I isdeliberately omitted) sequentially depict the effect of urging theshaped article 100 farther against the ram 300 in the directionindicated by the open arrow in each figure. In the embodiment shown inFIGS. 8H-8K, the deflectable flange 160 includes a peripheral flange 120at the peripheral end of the spacer 140. In these figures, it can beseen the peripheral flange 120 deflects during bending of thedeflectable flange 160 to the extent that it becomes completely bentover the spacer 140, forming a ‘hook’-like structure. B in FIG. 8Jindicates that bending is occurring in the portion of the deflectableflange 160 spanning the indicated portion of the upper face 302 of theram 300.

FIG. 9 consists of FIGS. 9A, 9B, 9C, 9D, 9E, and 9F and illustrates abeneficial feature of one embodiment of the shaped articles disclosedherein.

FIG. 9A is a cross-sectional view of one edge of an article 100 showingthe conformation of its deflectable flange 160 prior to the rolling-overoperation described herein, including the property that the potentiallysharp or rough peripheral edge 110 is accessible to contact a film usedto seal the article or another nearby film or object. FIG. 9B is across-sectional view of one edge of an article 100 have a peripheraledge 110 rolled over by the technique illustrated in FIGS. 8A-8C.Relative to the article engaged with the ram illustrated in FIG. 8C, thedeflectable flange 160 of the article has ‘rebounded’ in a peripheraldirection following disengagement from the ram. Because the plasticmaterial of which the article is constructed is flexible, therolled-over edge shown in FIG. 9B exhibits ‘springiness’ when urged indirections normal to the plane of the figure, such as in the directionsindicated by the open arrows.

FIG. 9C is a cross sectional view of the edges of three of the articles100 shown in FIG. 9B, the articles being stacked in a nestedconfiguration. Because each of the article has the same shapes (e.g., atray like the one shown in the lower portion of FIG. 6C), each articlecan nest and be urged together until with others its rolled-over edgecontacts the tray above and/or below it. FIG. 9C illustrates threethus-stacked nested trays, with open arrows indicating positions atwhich standard de-nesting equipment can be employed to separate thenested trays. Fingers or threads, for example, can engage the inter-trayregions at these positions, the fingers or threads being operable (perordinary de-nesting procedures) to separate the trays from one anotherfor individual use.

FIG. 9D is an image of a prior art thermoformed plastic tray having astacking lug (the corner extension beneath the rim, toward which thefinger in the image is pointing). The stacking lug serves to maintain acontrolled separation distance between stacked trays, as shown in theleft portion of FIG. 9E (which is an image of two of these prior arttrays stacked against one another, with the inter-tray distance beinglimited by the stacking lug). The right portion of FIG. 9E shows twostacked, nested trays having rolled-over edges (as illustrateddiagrammatically in FIG. 9C with three trays). An inter-tray division isvisible between the rims of the two stacked trays. FIG. 9E illustratesthat two trays having rolled-over edges as described herein can bestacked in a separable way in a smaller volume than can prior art trayshaving stacking lugs. FIG. 9F shows, on its left side, three nested andstacked trays having rolled-over edges and having stacking extensions180 formed into the corners thereof to increase separation between thestraight edges of the stacked trays. The three stacked trays havingstacking extensions 180 can be seen to have greater separation (largebrackets on left side of figure) than the separation (small brackets onright side of figure) of three otherwise-identical stacked trays lackingstacking extensions.

FIG. 10 consists of FIGS. 10A, 10B, and 10C. FIG. 10A is an image of aram 300 having a shaped article 100 in the form of a rimmed, roundedrectangular tray borne thereby. In the lower right portion of the imagecan be seen the upper surface 302 in which a second article could bedisposed, but which does not currently bear an article. In the article100 borne by the ram 300 in the upper part of the figure, it can be seenthat the extension 50 connects the spacer 140 and peripheral flange 120portions of the deflectable flange to the body 10 of the article 100.The spacer 140 and peripheral flange 120 are carried by the uppersurface of the ram 300 in the upper part of the figure, and that uppersurface (analogous to upper surface 302 in the lower right portion ofthe figure) cannot therefore be seen directly. “10B” indicates a portionof the ram 300 shown (with the shaped article 100 removed) in FIG. 10B.In FIG. 10B, portions of the upper surface 302 of the ram 300 can beseen. Dashed line 10C-10C in FIG. 10B indicates the approximate positionof the cross-section depicted in FIG. 10C, and letters A-E are includedas landmarks so that the surface configuration of the ram 300 can bebetter understood by comparing FIGS. 10B and 10C. FIG. 10C is adiagrammatic cross-section of the ram 300 shown in FIG. 10B, includinglandmark letters A-E.

FIG. 11 consists of FIGS. 11A, 11B, and 11C and illustrates features ofan embodiment of the shaped articles having a peelable liner sheetattached to a face of the article.

FIG. 11A is a cross-sectional view of an edge of an article thatincludes a relatively thick thermoformable substrate sheet 101 and arelatively thin, flexible liner sheet 500 attached to a face thereof,showing the conformation of the deflectable flange 160 of the articleprior to the rolling-over operation described herein, including itspotentially sharp or rough peripheral edge 110 at an accessibleposition. FIG. 11B is a cross-sectional view of the same edge of thisarticle after its peripheral edge has been rolled over as describedherein. The peripheral edge 111 of the substrate sheet 101 has beenrolled sufficiently that it “points back at” the body of the article,and the peripheral edge 511 of the liner sheet 500 has detached from (orbeen peeled away from) the peripheral edge 111 of the substrate sheet inthis view. In FIG. 11C, a sheet of lidding 600 contacts the liner sheet500 at the extension 50 portion of the deflectable flange, while aperipheral edge 610 of the lidding is positioned beyond the periphery ofthe article. The lidding 600 and the liner sheet 500 can be attached toone another by interposing an adhesive between them, or by pressing themagainst one another (e.g., while applying heat sufficient to bind ormelt them together), at the position indicated by the open arrow. If sobound to the liner sheet 500, the lidding 600 can be removed from thesubstrate sheet 101 of the article simultaneously with the liner sheet500 by grasping the liner sheet at or near its peripheral edge 511 andpeeling the liner sheet 500 (with the lidding 600 still attached) awayfrom the substrate sheet 101.

DETAILED DESCRIPTION

The subject matter disclosed herein relates to formation of shapedthermoplastic articles, and more specifically to articles which areformed such that one or more of the edges of the article has aconformation wherein the peripheral edge of a thermoplastic sheet fromwhich the article is formed is turned away from a face of the article,and preferably away from the periphery of the article, so that a fragilematerial (e.g., flesh or a thin, flexible plastic sheet) that is appliedagainst the face or periphery does not contact the edge of the sheet.Because such sheet edges can be sharp, especially when the edge has beencut or broken, directing the edge away from a face and/or periphery ofthe article can prevent damage to fragile materials which contact theface or periphery. The subject matter disclosed herein is of particularuse in forming containers which will be sealed with fragile plasticfilms applied against a face of the container or in which the containeris wrapped. In a preferred embodiment disclosed herein, the peripheraledge of the thermoplastic sheet from which the article is formed isturned away from the article's periphery so far that the resultingarticle is suitable for use in any or all of OW, VSP, and MAP sealingtechnologies. Desirably, thermoformable and moldable plastics tend to bewidely acceptable in recycling programs, and articles made therefrom canbe more readily recycled than, for example, foamed plastic articles.

Briefly summarized, the basic method described herein for forming ashaped thermoplastic article having a smooth edge involves forming adeflectable flange at the periphery of the article. The deflectableflange includes the potentially-sharp or -rough peripheral edge of thethermoplastic material from which the article is formed. The deflectableflange is softened (i.e., raised to a temperature at or above the glasstransition temperature of the material of which the flange is formed,and preferably a temperature less than the melting point of thematerial) at one or more portions thereof so that the peripheral edge isdirected away from the periphery of the article when the deflectableflange is deflected toward the body of the article (preferably ‘hiding’the peripheral edge between the deflected portion of the deflectableflange and the extension, the body, or both. Cooling (i.e., stiffening)the softened and deflected deflectable flange below its glass transitiontemperature “locks” the peripheral edge in that position, lessening thelikelihood that material (e.g. flesh or film) that contacts theperiphery of the article will be damaged by the sharpness or roughnessof the peripheral edge.

It is the presence of the deflectable flange formed at the peripherythat permits peripheral edges (and, particularly, curved edges andcorners of peripheral edges) to be “rolled over” to yield a smoothperiphery. In previous trays which included an exterior flange (e.g., atray having a periphery like that shown in FIG. 1A, lacking the bendregion 150, the spacer 140, the elbow 130, and the peripheral flange120, and having the peripheral edge 110 at the periphery of theextension 50), bending or rolling of the exterior flange might have beenpossible along straight edges, but bending or rolling curved edges andcorners of such exterior flanges could not be performed without bucklingor wrinkling of the material in the flange, yielding an undesirablenon-smooth edge. It is the presence of the smooth bend region 150 andthe spacer 140 of the deflectable flange described herein that permitsthe peripheral edge 110 to be deflected away from the periphery of thearticle without such buckling or wrinkling, yielding a smooth periphery.It can be seen from FIGS. 1, 4, 5, 7, and 8 that the bending, flexing,and curling that the deflectable flange undergoes can be effected in anyone or more of the extension 50, the bend region 150, the spacer 140,the elbow 130, the peripheral flange 120, and even at the peripheraledge 110. Whichever one or ones of these elements are caused to bend ordeflect in order to achieve the effect, the resulting disposition of thepotentially sharp peripheral edge 110 away from the periphery of thearticle, and preferably not reasonably accessible from the exterior ofthe article at its periphery yields an article having a smooth peripherywhich is suitable for contacting with fragile films, tissues, or othersurfaces.

In one embodiment, the deflectable flange includes a peripheral flangethat juts outs in a peripheral direction from the article and isattached to a spacer portion by way of an elbow (e.g., a 90-degree turnor a turn through some other offset angle, such as one of 60-120degrees) in the thermoplastic material that forms the article. The bodyof the article is attached to the spacer by way of a bend region, whichdefines an angle (angle A in FIG. 1A; preferably an approximately rightangle) between the spacer and the portion of the body adjacent the bendregion (i.e., this portion will usually be the extension which serves toconnect the body to the bend region). The deflectable flange is insertedinto the interior of a cavity in a body (e.g., an upper body 200 or aram 300) such that the peripheral flange is impinged by a wall ofcavity, thereby deflecting the deflectable flange in the direction ofthe body of the article. Upon such deflection, heat is applied to thebend region that is sufficient to soften or melt the thermoplasticmaterial at the bend region, so that the deflectable flange remainsdeflected toward the body when the bend region cools. Optionally, a ramcan be inserted into the cavity after the deflectable flange, and a faceof the ram which contacts the deflected peripheral flange can inducefurther deflection of the deflectable flange, further displacing theperipheral edge of the article away from the periphery of the articleupon cooling. In this way, a smooth, “rolled” edge of the thermoplasticmaterial forms the outermost periphery of the article, while theperipheral edge of the thermoplastic material remains within theoutermost periphery of the article, where the sharpness of that edge isless likely to damage fragile materials which contact the outermostperiphery of the article.

In another embodiment, the deflectable flange is contacted with a ramthat deflects the deflectable flange in a direction that deflects thesharp edge of the thermoplastic sheet away from the periphery of thearticle. Before, during, or after such deflection, one or more portionsof the deflectable flange (e.g., the bend region, the spacer, the elbow,the peripheral flange, any portion(s) that contact the ram, or acombination of these) are heated sufficiently to soften thethermoplastic material, and the deflectable flange is thereafter cooledto “lock in” the deflection. Depending on the degree of deflection, theperipheral edge of the thermoplastic material can be simply turned awayfrom the periphery of the article, turned in a direction approximatelyopposite the periphery, or even “rolled up” by deflecting thedeflectable flange at a sufficiently tight radius while it is softenedthat a J-shaped, U-shaped, or even spiral-shaped conformation isachieved (i.e., any shape yielding a substantially smooth peripheraledge), with the peripheral edge being thereby rendered virtuallyincapable of damaging flesh or film present at the periphery of thearticle.

Individual elements and aspects of the shaped articles and methods formaking them are now described in greater detail.

The Shaped Article

The methods described herein are believed to be applicable to articleshaving a wide range of shapes and sizes, especially articles whichnormally have a sharp peripheral edge when made by common methods.Motivation for making shaped thermoplastic articles with smooth edgesstemmed in part from a desire to make common storage trays (e.g.,plastic trays used for storing foodstuffs such as fresh or frozen meats,fruits, or vegetables) having edges that are sufficiently dull(non-sharp) that the trays can be wrapped in or contacted with thinplastic films such as polyvinylidene chloride and polyethylene filmswithout the film being cut or punctured by the tray edge under normalusage conditions. However, once the methods described herein weredeveloped, it was recognized that the smooth, rounded edges aredesirable in a variety of other situations, such as preventing injury tothe flesh of humans handling trays and other shaped articles andpreventing damage to films sealing one tray by sharp edges of a secondsealed tray (e.g., as in a shipping container containing multiple sealedtrays).

By way of example, a common method of making shaped articles such asmeat trays is by thermoforming a sheet of a thermoplastic. Inthermoforming processes, a portion of a long sheet of a thermoplastic israised to a temperature at which the thermoplastic softens and can bemolded. The softened thermoplastic is applied against the surface of oneor more molds (often with the aid of negative air pressure to ensure atight opposition of the softened thermoplastic film against the moldsurface). As the film cools (e.g., upon contact with the mold surface),the thermoplastic hardens and becomes less easily deformable, resultingin the thermoplastic film attaining and retaining the shape imposed uponit by the molding process. Multiple casts are often made of the samearticle in a single sheet of film in thermoforming processes, and theindividual articles are freed from the film by cutting (e.g., diecutting) the film about the periphery of the article. This process tendsto yield a sharp edge at the cut portions of the film, including a sharpedge that surrounds all or a portion of the periphery of the article(i.e., where the article was cut from the film).

Further by way of example, a thermoplastic material can be melted in anextruder and injected into a mold cavity which defines the shape of themolded article. After cooling, the mold can be opened to release themolded article. In molding processes, it is common for thermoplasticmaterial to appear at parts of the finished articles where it is notdesired, such as “flashing” that occurs when molten thermoplastic flowsbetween mold plates or at the ports through which the moltenthermoplastic was fed into the closed mold. These non-desired parts canbe sharp in their own right, and sharp edges can be left when thesenon-desired parts are cut from the molded article.

The size and shape of the articles described herein are not critical. Ingeneral, the shaped articles will be ones for which handling of thearticles or contact between peripheral edges of the article and one ormore fragile materials is anticipated. The edge-smoothing processdescribed herein can remove one or more sharp edges from thermoplasticarticles which normally have such sharp edges, regardless of themethod(s) by which the articles are produced.

The Smoothing Method

The periphery of a thermoplastic article—particularly one formed from abent or shaped sheet of a thermoplastic material—can be smoothed by aprocess that includes forming a deflectable flange near the periphery ofthe edge to be smoothed, deflecting a bent portion of the flange todisplace the edge from the periphery of the article, softening the bentportion at least while the flange is in the deflected position, andre-hardening the bent portion while the flange is in the deflectedposition. This process is illustrated in FIG. 1. The portion of thedeflectable flange 160 that can be softened and bent can be the bendregion 150 or, preferably, a portion of the deflectable flange distal tothe bend region 150, but proximal to the peripheral edge 110. By way ofexample, softening the spacer 140 permits its peripheral portion,including the elbow 130, peripheral flange 120 (if these two elementsare present), and peripheral edge 110 to be bent inwardly (i.e., towardthe body 10 of the article 100) sufficiently to displace the peripheraledge 110 away from the periphery of the article.

Preferably, at least a portion of the spacer 140 is softened and bentsufficiently that the peripheral edge 110 is “rolled over,” such thatthe peripheral edge 110 is positioned such that a film that overwrapsthe article or that is draped across the article does not contact theperipheral edge 110, even if pulled taut. Still more preferably, thedeflectable flange 160 is rolled over sufficiently that the peripheraledge 110 is visually obscured by the spacer 140 or the bend region 150such that the peripheral edge 110 cannot be seen when the article 100 isviewed horizontally from it periphery (i.e., from its peripheral side).Also preferably, the deflectable flange 160 is rolled over sufficientlythat the peripheral edge 110 “points” toward the body 10 or toward theunderside of a portion of the deflectable flange 160, meaning that theplane of the deflectable flange at the portion including its peripheraledge 110 intersects the body 10, including the underside 161 of theperipheral edge. When the plane of the deflectable flange at its edgeincluding the peripheral edge 110 does not point at the body 10 or theunderside 161, then that peripheral edge should at least be displacedfar enough from the periphery of the article 100 or rolled oversufficiently to obscure the peripheral edge 110 by one or more portionsof the deflectable flange 160.

FIG. 1A illustrates a thermoplastic article 100 having a body 10 (with,in this figure, an irregular shape) and a deflectable flange connectedwith the body 10. The deflectable flange includes a peripheral flange120 which includes a peripheral edge 110 of the thermoplastic sheet fromwhich the article 100 is formed. The deflectable flange also includes abend region 150 interposed between the body 10 of the article 100 andthe peripheral flange 120. The bend region 150 is separated from thebody 10 by an extension 50, which is simply a flat portion of thethermoplastic sheet in this embodiment. The peripheral flange 120 issimilarly separated from the bend region by a flat portion of thethermoplastic sheet designated the spacer 140 in this embodiment. Theperipheral flange 120 is connected to the remainder of the deflectableflange by an elbow 130 which, in this embodiment, is a portion of thethermoplastic sheet formed into a right angle.

FIG. 1A is a cross-section of such an article 100, in which the solidblack line represents the cross-section of the thermoplastic sheet fromwhich it is formed. The peripheral edge 110 forms the periphery of thearticle 100 because no other portion of the article 100 extends fartherto the right (in this figure), the spacer 140 and the other portions ofthe peripheral flange 120 being nearer to the body 10 than theperipheral edge 110 of the sheet. Thus, if an object were urged againstthe right side (in FIG. 1A) of article 100, the object would tend tocontact peripheral edge 110 and the sharpness of that peripheral edge110 could affect the object, such as by cutting, damaging, or injuringthe object.

In FIG. 1B, the thermoplastic article 100 is inserted within an interiorcavity of an upper body 200. The inner surface 202 of the upper bodyimpinges upon the peripheral flange 120, deflecting it inwardly (i.e.,anti-peripherally) toward the body 10 of the article 100. In thisembodiment, both the peripheral edge 110 of the thermoplastic sheet fromwhich the article 100 is formed and the peripheral-most portion of thebend region 150 are positioned about equally peripherally from the body10. Preferably, the deflectable flange 160 is deflected inwardlysufficiently far that the peripheral edge 110 of the thermoplastic sheetis contained within the interior cavity of the upper body 200. In thisembodiment, the spacer 140 is essentially rigid and substantially allbending occurs within the bend region 150. If heat sufficient to softenthe thermoplastic sheet is applied to the bend region 150 (atapproximately the location identified as “B” in FIG. 1B) and the sheetis subsequently cooled (preferably below its glass transitiontemperature), then the deflectable flange 160 will retain theconfiguration shown in FIG. 1B (i.e., deflected relative to its initialconformation shown in FIG. 1A on account of impingement of theperipheral edge 110 against the inner surface 202 of the upper body 200)even after upper body 200 is separated from the article 100. In thisdeflected conformation, the peripheral edge 110 does not extendperipherally beyond the rounded bend region 150, and the resultingarticle will be more suitable for sealing with a thin plastic filmapplied to extension 50 and bend region 150 than was the original,pre-deformation article shown in FIG. 1A (i.e., on account of theprotuberance of potentially sharp peripheral edge 110 beyond theperiphery of bend region 150, at which position the peripheral edge 110might readily snag, abrade, or cut the film).

FIG. 1C illustrates an optional, but preferable step in which a ram 300is inserted within the cavity in the upper body 200 behind the article100 (i.e., sandwiching at least the deflectable flange 160 between theupper body 200 and the ram 300). This step further deflects (relative tothe embodiment show in FIG. 1B) the deflectable flange 160 towards thebody 10 of the article 100, thereby displacing the (potentially sharp)peripheral edge 110 of the thermoplastic sheet further from theperiphery of the article (i.e., farther from inner surface 202 of theupper body 200). Heating the bend region 150 of the deflectable flange160 sufficiently to at least soften it while it is in the conformationshown in FIG. 1C and subsequently cooling it below its glass transitiontemperature will ‘freeze’ the deflectable flange in the conformationshown. In this conformation, the sharp peripheral edge 110 of the sheetfrom which the article is formed is ‘tucked’ under other portions (e.g.,the bend region 150 and the extension 50, if present) of the deflectableflange 160, and is consequently less accessible to objects contactingthe periphery of the article (and less liable to tear, cut, or injurematerials which contact the periphery of the article). For example, if athin plastic film is applied to extension 50 and bend region 150, thenthe film is even less likely to be snagged, abraded, or cut by thepotentially sharp peripheral edge 110 in this embodiment than it was inthe embodiment shown in FIG. 1B. From this progression (i.e., greaterdeflection in FIG. 1C than in FIG. 1B and FIG. 1A), it can be seen thatthe more the peripheral edge 110 is deflected away from the periphery ofportions of the article to which a sealing film is applied, the lesslikely damage to the film from the edge becomes.

The ram 300 and the upper body 200 each serve the purpose of deflectingthe deflectable flange by impacting upon or against it. These two itemsare therefore essentially interchangeable and can each be used alone orin combinations two or more ram(s) and upper body(ies). In thisdisclosure, the term “ram” is used to refer to a body that impinges uponthe deflectable flange by being applied thereto or thereagainst in adirection from the portion of the deflectable flange most distal fromthe body of the shaped article. Similarly, the term “upper body” is usedto refer to a body that impinges upon the deflectable flange by beingapplied thereto or thereagainst in about the opposite direction (see,e.g., FIGS. 1C and 4).

In the example shown in FIG. 1C, the portions of the ram 300 whichimpinge upon the peripheral flange 120 of the deflectable flange 160while the article is lodged within the cavity in the upper body 200 hasa wedge-shaped cross section. Such a ram can be useful for directing theperipheral flange 120 and peripheral edge 110 anti-peripherally, in thatthe farther the ram is advanced within the interior in the directionfrom the peripheral edge 110 toward the bend region 150, the farther theperipheral flange 120 and peripheral edge 110 will be deflected in ananti-peripherally direction. However, these portions of the ram 300 neednot be wedge-shaped. Substantially any shape of ram 300 that willdeflect the peripheral flange 120 and peripheral edge 110anti-peripherally when the ram 300 is inserted behind the article 100 inthe upper body 200 can be used, such as blunt or rounded (convex orconcave at its upper face 302), or a combination of any of these, can beused, for example as shown in FIG. 5.

FIG. 8 illustrates an alternate method of rolling or otherwise shapingthe edge of an article. As can be seen in FIG. 8A, the deflectableflange 160 in this embodiment lacks an elbow or peripheral flange, andinstead includes only a spacer portion that terminates at the peripheraledge 110 of the thermoplastic sheet. This deflectable flange is urged(in the direction indicated by the open arrows in FIG. 8, regardless ofhow such urging is achieved, such as by moving either or both of thearticle 100 or the ram 300) against the upper surface 302 of a heatedram. When the direction of travel of the deflectable flange closelyparallels the conformation of the upper surface (i.e., as in FIG. 8A),relatively little of the deflectable flange may contact the uppersurface and relatively little heat may be transferred from the ram tothe deflectable flange. However, as shown in FIG. 8B, when relativemovement of the article and the ram cause greater surface contact orgreater proximity between the upper surface of the ram and thedeflectable flange, the interfacial area of contact/proximity can begreater, resulting in greater heat flow from the ram to the deflectableflange. Sufficient heat flow will result in softening of thethermoformable material, causing the deflectable flange to assume theconformation of the upper surface. When, as shown in FIG. 8C, stillfurther relative movement of the article and the ram is made, a greaterportion of the deflectable flange will be softened and deflected. Aswith the embodiment shown in FIG. 1B, it can be seen in this embodimentthat heat suitable for bending the deflectable flange is being applied(at multiple locations B in FIGS. 8B and 8C); however, in order to “rollover” the portion of the deflectable flange that includes the peripheraledge, little or no flexion, and no heat application, is occurring at thebend region 150 (other than perhaps to a small degree as theperipheral-most portions of the bend region 150 approach the heated ram300, as in FIG. 8C). For the purposes of the processes described herein,it is substantially immaterial which portions of the deflectable flangeare softened and bent, so long as the desired result is obtained: thepotentially sharp peripheral edge 110 is deflected away from theperiphery of the article and, preferably, sequestered (as in FIG. 8C)where it is very unlikely to contact any easily-damaged film or tissuewhich contacts the periphery of the shaped article. The deflectableflange can be contacted with, or brought into close proximity with, theram in a single smooth motion, in a plurality of discrete, incrementaladvances, or a combination of these, in order to permit portions of thedeflectable flange to soften sequentially.

As the thermoformable material moves out of contact with the ram (eitherby disengaging the two or, as shown in FIG. 8C as a portion of thedeflectable flange moves beyond the upper surface of the ram), thethermoformable material can cool and the deflection induced therein willbe retained upon cooling. As shown in FIG. 9A, disengagement of thearticle and the ram results in a rolled-over edge of the article, therolled-over edge having a smooth periphery and being suitable forhandling and/or contact with fragile plastic films.

In FIG. 8A-8C, the deflectable flange was depicted lacking the elbow 130and peripheral flange 120 illustrated in FIG. 1A for the sake ofsimplicity of illustration. Although production of deflectable flangeslacking the elbow and peripheral flange is possible (e.g., bymechanically or laser-cutting the deflectable flange at the spacer 140shown in FIG. 1), such production can be difficult and costly and istherefore of limited practicality in large-scale production operations.For this reason, shaped articles 100, such as those intended for use aspackaging trays for food, that are processed described herein will oftenhave both the elbow and peripheral flange illustrated in FIG. 1A. Asillustrated in FIGS. 8E-8K, shaped articles bearing the elbow andperipheral flange can nonetheless be processed using the methods andequipment described herein.

FIGS. 8E-8G depict processing of a shaped article 100 that has adeflectable flange 160 that includes both the peripheral flange 120 andthe elbow 130 described herein, and the processing depicted in thesefigures is roughly analogous to that depicted in FIGS. 8A-8C. In FIG.8E, the peripheral edge of the deflectable flange 120 directly contactsthe upper surface 302 of the ram 300. Because the ram is heated, heat isconducted directly to the peripheral edge where it contacts the ram andby radiation from closely-opposed portions of the spacer 140. Bycontrolling heat flowing from the ram and the residence time of thearticle 100 in the position shown in FIG. 8E, an operator can inducesoftening of portions of the deflectable flange, particularly includingat its peripheral edge and at portions of the spacer near thatperipheral edge. Softening of these portions facilitates bending of thedeflectable flange at the softened portions, such as by urging thearticle further against the ram, such that a curved portion of the uppersurface will induce bending as the more-peripheral portions of thedeflectable flange are driven against the curved portion of the uppersurface by the less-peripheral portions (which transmit force applied tothe article), as shown in FIG. 8F. Further urging of the article againstthe ram, as shown in FIG. 8G, causes the portions of the deflectableflange that are in contact with the upper surface of the ram to slideacross that upper surface. As material is driven beyond positions inwhich it is in contact with the upper surface, it may remain softened(and susceptible to further bending) for a short period of time, or itmay cool and become only deflectable (rather than bendable or moldable).Whether cooled by movement past the heated portion(s) of the ram or byremoving the article from contact with the ram (or even by appliedcooling, such as by directing cool air at shaped portions, by using acooled plug element within the body of the article, or otherwise),cooling of the deflectable flange below its glass transition temperature“sets” or “locks in” the conformation of the material at the time ofthat transition. Thus, by shaping the deflectable flange so that it hasthe conformation shown in FIG. 8G and cooling it below its glasstransition temperature, the edge of the article can be rendered smooth(both because its bend region 150 is smooth and because its spacer 140,including its peripheral edge 110 have been changed to have aconformation in which no rough or sharp edges are present at theperiphery of the article.

As shown in FIG. 8F, the peripheral flange 120 can be partiallydeflected during shaping of the deflectable flange; in the finishedarticle, the peripheral edge preferably “points” toward the body or theunderside of the deflectable flange. As shown in FIG. 8G, shaping of thedeflectable flange will sometimes result in disappearance of theperipheral flange and the elbow interposed between it and the remainderof the spacer. This can occur because the material in the peripheralflange “melts” into the spacer or simply because the offset angle of theelbow becomes approximately 180 degrees. As can be seen in FIG. 8J, forexample, though, the peripheral flange 120 can deflect in a directionthat it remains distinct from the remainder of the spacer, potentiallyforming a hook-like structure. Because such a structure could positionthe potentially-sharp or -rough peripheral edge at or near the peripheryof the article, it is preferable that the deflectable flange bedeflected sufficiently that any such hook-like structure is containedwithin (relative to the periphery of the article) the rolled-over edge,as illustrated in FIG. 8K.

In the methods illustrated in FIGS. 1 and 8, impingement of the upperbody 200, the ram 300, or both upon the deflectable flange 160 caninduce inward flexing of the walls of the shaped article. By way ofexample, the compression induced in the deflectable flange uponimpingement upon the flange of the sidewalls of the upper body (comparethe positions of spacer 140 in FIGS. 1A and 1B) will induce inward(i.e., away from the sidewalls of the upper body and toward the shapedbody 10 of the article 100) force on extension 50, which force will betransmitted to the shaped body, potentially causing a portion of thebody to buckle or deflect. Similarly, impingement of the ram upon theperipheral flange portion 120 of the deflectable flange will also induceinward force on the extension and thereby upon the shaped body. Furtherby way of example, inward force exerted upon deflectable flanges inembodiments shown in FIGS. 7 and 8 can also be transmitted to the shapedbody of the article. Transmission of force from the deflectable flangeto the shaped body can be undesirable for at least two reasons. First,deflection of the shaped body can alter the orientation of thedeflectable flange and the portions that are bent as described herein,making control of the final shape of the article (and its edge)difficult. Second, force that is transferred from the deflectable flangeto the body will generally not drive the deflectable flange against theram and/or upper body, meaning that the force will not cause the bendingand deflection of the deflectable flange described herein, at least tothe intended degree. It is therefore desirable to limit transmission offorce from the deflectable flange, deflection of the shaped body by suchforces, or both, so as to direct the force into deflection of thedeflectable flange.

Substantially any equipment or method for preventing or reducingtransmission of force from the deflectable flange to the body, reducingor preventing deflection of the shaped body, or both can be employed.Shown in FIG. 8D is an example of such equipment and how it is used.FIG. 8D illustrates shaping of the deflectable flange 160 in a shapedarticle 100 by application of downward force (open arrow), as shown inFIG. 8B. In contrast with FIG. 8B, the shaped article shown in FIG. 8Dis coupled with three objects, 401, 402, and 403. Shown here incross-section, each of the three objects is a solid having a roundedsquare profile (e.g., rounded metal bars). Object 401 is abutted againsta portion of the shaped article 100 upon which inward force (smaller,horizontal solid arrow) is applied when the downward force causes thedeflectable flange 160 to impinge upon the upper surface 302 of the ram300. Object 403 abuts the extension 50 of the deflectable flange andtransmits the downward force to the deflectable flange. Object 402connects (rigidly, in this example, but not necessarily) objects 401 and402. One or more of the three objects can be cooled, to prevent heat(e.g., from heated ram 300) from softening the plastic at its body orextension.

In FIG. 8D, when downward force (open arrow) is applied to the object403, the force is transmitted to the deflectable flange. Impingement ofthe deflectable flange upon the ram 300 opposes the downward force. Thisforce could, in the absence of object 401 be transmitted through thedeflectable flange (i.e., through extension 50) to the shaped body ofthe article 100. However, because object 401 is present and held inplace sufficiently to prevent deflection of the portion of the articleit abuts, downward force applied to the deflectable flange cannot bedissipated by deflection of the shaped body (i.e., in the directionindicated by the small horizontal black arrow in FIG. 8D, because object401 prevents such deflection), and the downward force is instead imposedalong the deflectable flange in the direction shown by the large blackarrow in FIG. 8D. This force drives the deflectable flange (particularlyits peripheral edge, the peripheral flange if present, and the portionof the spacer nearest the peripheral edge) against the ram 300 andinduces deflection of the deflectable flange, conformation of portionsof the deflectable flange against the upper surface 302 of the ram(especially when the amount of heat provided by the ram is sufficient tosoften those portions), and displacement of the deflectable flangeacross the surface of the ram. As shown in the figure, the contour ofthe upper surface of the ram is thereby imparted to the peripheral-mostportions of the deflectable flange, resulting in smooth bending of thoseportions (assuming a smooth contour to the upper face of the ram) anddisplacement of the peripheral edge of the deflectable flange toward thebody of the article (or even ‘curled’ back beyond the body, for exampleas shown in FIG. 8C).

The shape, size, arrangement, attachments (if any) of objects 401, 402,and 403 are not critical. Likewise, not all three objects neednecessarily be used together; one, two, or all three can be employed. Inone embodiment, the three objects are fixed together to form a “lid” or“plug” for a container like that shown in FIG. 6, so that the portion ofthe lid/plug that corresponds to object 401 can substantially fill theinterior of the container (i.e., pressing against all walls, andespecially including the four long, straight walls of the container),the portion of the lid/plug that corresponds to object 403 forms a ringthat can be applied against the entire rim of the container surroundingits interior, and the portion of the lid/plug that corresponds to object402 can be any material or mechanism that connect them. For example,such a lid/plug could be formed from a single piece of material (e.g., a‘plug’ that fills the entirety of the interior and overlaps the rimsurrounding the interior). One or more of the objects can be cooled toreduce heating of the shaped article (other than where desired, atportions of the deflectable flange) and to thereby prevent undesireddeformation of the shaped articles during processing.

Generalized, object 401 is simply a mass for preventing flexing of thesides of the shaped article during deflection of the deflectable flange.Such an object may fill substantially all portions of the interior ofthe shaped article (e.g., the entire interior of the container shown inFIG. 6D). Alternatively, one or more objects 401 may be used to buttressportions of the shaped article that are more easily deflected thanothers (e.g., the long straight sides of the container shown in FIG.6D).

Object 403 can be any object that can urge the deflectable flangeagainst the ram. Multiple objects can be used to urge the deflectableflange against one or more rams at various locations on the article, ora single object 403 that contacts the article at or near all portions ofthe deflectable flange can be used. In one embodiment, object 403 is theupper body 200 described herein, such as in the form that completelysurrounds the rim of a container such as that shown in FIG. 6D. Object403 can be a frame designed to fit snugly against the entire rim of acontainer surrounding an internal concave compartment of the chamber, soas to simultaneously urge a deflectable flange that completely surroundsthat rim against a ram in the manner described herein. In oneembodiment, object 403 can be deliberately cooled (e.g., by directing acooling fluid such as chilled water, chilled oil, or ambient air againstor through the object, particularly where the object is made of a goodconductor of heat, such as a metal) so as to reduce, inhibit, or preventheating of the body of the shaped article during processing (e.g., asshown in FIG. 8D). Object 403 can be linked, rigidly or movably, withobject 401 so that the flex-resisting object 401 can be applied to theinterior of a shaped article simultaneously with application of force tothe deflectable flange of the shaped article by object 403.

Object 402, when present, can be an object that connects object 403 to asource of force, an object that holds object 401 in place within aconcave portion of shaped article 100 during deflection of deflectableflange 160, or a combination of these.

As illustrated in FIGS. 9C and 9E, an additional advantage of therolled-over edge formed by this process is that the rolled edge can beused instead of conventional stacking lugs (i.e., thermoform-shapedportions of articles contoured to limit how closely an article can nestwithin another otherwise-identically shaped article). Such knownstacking lugs, in order to perform their desired anti-nesting function,must furthermore be narrower at their upper end than their lower end(referring to FIG. 9D as an example) in order to prevent nesting of thestacking lugs of adjacent trays. This ‘narrower-at-the-top’ conformationpresents known difficulties with de-molding the trays duringthermoforming, since the narrower ‘top’ portion of the lug must bestretched or deformed over the larger ‘bottom’ portion of the lug moldin order to remove the thermoformed tray from the mold. The rolled edgedepicted in FIGS. 8 and 9 (i.e., made as described herein) avoids thisdifficulty, while still preventing inappropriately close nesting ofadjacent trays. Trays having the rolled edge described herein can beseparated using conventional de-nesting equipment (e.g., screw- andfinger-based machines for separating adjacent nested/stacked trays) and,as shown in FIG. 9E, permit denser packing of trays than is possibleusing trays having formed stacking lugs.

FIG. 9F illustrates an optional embodiment of the rolled edge describedherein that also affects the stacking characteristics of shaped articleshaving the rolled edge. On the right side of FIG. 9F are shown threestacked trays having the rolled edge described herein, the rolled edgebeing substantially identical (including in height) about the entireperiphery of the tray. On the left side of FIG. 9F are shown three otherstacked trays, these trays also bearing a rolled over edge as describedherein about their entire periphery. However, in contrast to the trayson the right of the figure, the rolled edge of those on the left are notuniform about their entire periphery. As shown in the figure at onecorner, a smaller portion of the deflectable flange has been rolled overat the corners of these trays than the portion of the deflectable flangethat is rolled over along other portions of their edge. As a result, thetrays bear rounded stacking extensions 180 at their corners. Like thatstacked trays shown on the right of FIG. 9F, those on the left of thefigure are nested within one another and settle until the lower surfaceof the rolled edge of a tray contacts and rests upon the upper surfaceof the rolled edge of a second tray within which it is nested. However,because the stacking extensions 180 of the trays on the left of thefigure have a greater height than much of the rest of the rolled edge ofthose trays, the trays on the left will nest such that the lower surfaceof a stacking extension 180 rests on the upper surface of the rollededge of a tray beneath it, leaving the lower surface of much of therolled edge of the upper tray out-of-contact with the tray beneath it,yielding a gap between the nested trays (compare the gap indicated bythe large brackets in the left of FIG. 9F with the indentation indicatedby the small brackets in the right of FIG. 9F). When a shaped article100 is given a rolled over edge including a stacking extension 180 asdescribed herein, the degree to and way in which the deflectable flangeis deflected should nonetheless be selected to position the peripheraledge 110 at the stacking extension 180 such that it is unlikely tocontact films or other materials at the periphery of the article 100, asdescribed herein.

Yet another advantage of the ‘rolled edge’ depicted in FIGS. 8 and 9 isthe mechanical strength imparted to a shaped article by such an edgeconformation. Thin plastic films tend to be highly flexible, andarticles formed from such films can have ‘flimsy’ edges that are easilydeformed upon handling or manipulation (e.g., during sealing or wrappingwith film). For the same reasons that hollow tubes or rounds of materialtend to be stronger and more rigid than planar sheets of material of thesame type and thickness, the curved or rolled edge described hereinconfer greater edge strength and rigidity to the shaped articlesdescribed herein than corresponding articles lacking such an edge. Thisedge strength and rigidity permits formation of lids upon, or engagementof separately-made lids with shaped articles described herein. Thus, inaddition to the shaped articles being sealable with film using OW, VSP,or MAP technologies, the enhanced edge strength of the shaped articlesdescribed herein permits them to be sealed with snap-on/snap-off typelids or other conventional sealing technologies. The edge strength andrigidity conferred to the shaped article also prevents deflectioninduced by tension in a film used to overwrap or seal the article (e.g.,so-called “bow-tying” as the phenomenon of a concave article closingupon its concavity when wrapped or sealed) and to withstand stressesimposed by (or necessary to the operation of) container-handlingequipment, such as de-nesting equipment used for segregating individualcontainers from a stack of nested containers.

What is important in these methods is that the potentially sharpperipheral edge 110 of the thermoplastic sheet(s) from which the article100 is formed should be deflected away from the periphery of the articleand ‘frozen’ in that position by heat-softening and cooling a portion ofthe sheet that is bent (which will normally include substantially onlyportions of the deflectable flange) while the sheet is so deflected. Theheated, bent, and cooled region preferably includes at least the bendregion 150 of the deflectable flange 160, because that region isdesigned for smooth flexing and yields a smooth periphery to thecontainer. Softening, flexing, and hardening of other portions of thedeflectable flange (e.g., the extension 50, spacer 140, elbow 130,and/or peripheral flange 120) can also (or alternatively) be done, andcan contribute to smoothness of the article's periphery.

Alternatively, any of these portions of deflectable flange 160 cansimply be bent without heating, so long as sufficient bending force isapplied that the thermoplastic material irreversibly bends (rather thanmerely reversibly deflecting upon removal of pressure) at the bentlocation. However, non-heating-and-softening-based bending methods willtend to leave relative sharp (or, at least, less smooth) edges wherebends are imposed, and so such methods are not favored unless care istaken (e.g., by bending materials about a rounded ‘mold’ member) toensure that such bends are smooth. The deflectable flange 160 disclosedherein provides a convenient structure for practicing this method.

The Deflectable Flange 160

The deflectable flange includes a bend region 150, a peripheral edge110, and a spacer 140 interposed between the two. The bend region formsan angle of less than 180 degrees between the body 10 and the spacer 140and functions as a flexible ‘hinge’ at which the spacer region can bedisplaced relative to the body. The angle formed by the bend region(i.e., the angle designated A in FIG. 1A) is preferably about ninetydegrees (i.e., approximately a right angle, meaning not less than 75 normore than 105 degrees, more preferably not less than 85 nor more than100 degrees, still more preferably not less than 87 nor more than 93degrees, and most preferably about 92 degrees). When this angle is lessthan 90 degrees, it can be difficult to remove the thermoformed articlefrom the thermoforming mold (i.e., because the portion of the moldnearest the extension between the spacer and the body can be broaderthan the width between the body and the spacer nearer to the peripheraledge, meaning that the thermoformed article will ‘grip’ the mold andmust be pulled or expanded to displace it from the mold). Thus, it ispreferable that the angle formed by the bend region is 90 degrees orgreater (e.g., 91, 92, 93, 94, or 95 degrees) to ease separation of thethermoformed article and the mold, but the angle can be smaller if thebody of the article recedes away from the periphery, for example. Lesspreferably, an angle of 110, 115, 120, 125, 130, or 135 degrees can beemployed, but such articles may require application of both an upperbody 200 to reduce the angle near to 90 degrees prior to impacting thedeflectable flange against the ram 300. As this angle increases, theamount of thermoplastic that is present at exterior corners (e.g., thefour corners of the tray shown in FIGS. 6A and 6B) of the thermoformedprecursor article increases and can interfere with bending (i.e.,“rolling-over”). This thermoplastic material can be accommodated, forexample, by permitting the spacer to ‘bow out’ above the ram (or into aspace built into the upper surface of the ram) at sections where thematerial occurs.

Upon sufficient displacement of the spacer, the bend region forms theperiphery of the article (i.e., when the spacer is bent “under” theconnected portion of the body, regardless of orientation relative togravity). Thus, the bend region will normally form the smooth peripheryof the article that is desired in one embodiment. The spacer nonethelessforms a part of the periphery of the article in this embodiment(normally the “underside” of the periphery, relative to the article 100,with the underside 161 of the deflectable flange 160 being containedwithin the curvature of the rolled-over edge). For this reason, portionsof the spacer (potentially including the elbow 130 and the peripheralflange 120) that are reasonably accessible to a film or other materialpressed against the exterior of the article (e.g., against the undersideof its periphery) should preferably be smooth as well.

In formation of the shaped articles with a smooth periphery describedherein, deflection of the spacer (and/or other portions) of thedeflectable flange induces bending within the bend region, within thespacer, or both. The angular shape of the bend region both controls thelocation of that bending and the smoothness of the resulting edge. Asillustrated in FIGS. 1 and 8, it can be beneficial if the angularportion of the bend region is not formed as a sharp (i.e., bi-linear)angle, but is instead formed as flat portions (e.g., an extension 50 anda spacer 140) arranged at an angle to one another, with a curved portion(e.g., defined by a radius of curvature, such as a radius of 1, 2, or 3or more millimeters) connecting the flat portions. Flexing of a curvedangular portion will tend to yield a smoother, less film-damaging edgethat flexing of a sharply angled portion. As illustrated in FIGS. 1, 4,5, 7, and 8, the boundary between the bend region 150 and the spacer 140may be substantially indistinguishable in practice, and flexion of thespacer 140, at least at its extent nearest the bend region 150 isexpected in the embodiments shown. As illustrated in FIG. 8 especially,bending of multiple portions, including the peripheral-most portion(s),of the spacer 140 can desirably impart a smooth periphery to thearticles prepared as described herein.

In one embodiment (shown in FIG. 1), the deflectable flange 160 includesat least three portions, including the bend region 150, a peripheralflange 120, and an elbow 130 positioned therebetween. The bend region150 is connected to the remainder of the article 100, optionally by wayof an extension 50. The peripheral flange 120 is connected to the bendregion 150 by way of the elbow 130, optionally with a spacer 140interposed between the bend region 150 and the elbow 130. A prototypicaldeflectable flange 160 having each of these portions is illustrated(attached to the body 10 of an article 100) in FIG. 1A.

In this embodiment, the bend region 150 is situated anti-peripherally(nearer the body 10) than at least the peripheral-most portion of theperipheral flange 120. The function of the bend region 150 is to deflectwhen the peripheral flange 120 is deflected inwardly (i.e.,anti-peripherally, such as by pressing the periphery of the articleagainst a solid object). Deflection of the bend region provides a smoothsurface because the peripheral edge 110 of the thermoplastic sheet isnot located within the bend region; it is located on the peripheralflange 120. The angle formed by the bend region (for example,approximately 90 degrees over the bend region 150 shown in FIG. 1A) isnot critical, and can be selected for ease of manufacture. It can, forexample, be an obtuse angle, a right angle, or even an acute angle. Whenthis angle is an acute angle, it can be difficult to remove thethermoformed (pre-roll-over) article from its thermoforming mold(because the peripheral portion of the spacer must be deflected toremove the article from the mold), and acute angles are disfavored forthat reason (even though such articles can still be made). The radius ofcurvature of the bend region 150 is also not critical, although it ispreferably substantially greater than the radius of curvature of theelbow 130.

The bend region 150 preferably has the conformation of a smooth curve,as shown in FIG. 1A, with a substantial radius of curvature (e.g., 0.5millimeters to several millimeters or more), so that inward deflectionof the deflectable flange 160 yields a smooth periphery to the article.However, it is critical that the bend region 150 simply not be sharp orpointed; a non-sharp crease can suffice, for example. Fragile materials,such as thin plastic films or animal skin, which contact that smoothperiphery are much less likely to be damaged than when the same fragilematerials contact the peripheral edge 110 of the thermoplastic sheet.

The bend region 150 can be connected with the remainder of the article100 by way of an extension 50. The extension 50 can be discretelydiscernible from the bend region 150 (e.g., a flat region distinct froma curved bend region 150) or substantially indistinguishable (e.g., aslightly curved region not readily distinguished from the curvature ofthe bend region 150). The dimensions of the extension region are notcritical; it can range from non-existent (i.e., the bend region 150commences at the edge of a body 10 of the article 100), to a fraction ofa millimeter, to several millimeters or longer. One function of theextension 50 is to separate the bend region 150 (at whichsheet-softening heat is applied in some embodiments) from other portionsof the article 100 at which potential heat-induced deformation isundesirable. Another function of the extension 50 can be to provide afunctional surface to the article 100, such as a surface adjacent thebend region 150 at which a thin plastic film (which can be pressedagainst the bend region 150 with little danger of damage to the film)can be adhered to or fused with the article 100 (e.g., to cover a cavityformed in the article that is bordered by the deflectable flange 160 ofwhich the extension 50 is part). The extension 50 can also serve astructural function, such as providing support or rigidity to a sectionof the article (e.g., by forming a relatively rigid “rim” about a cavityin a container to inhibit flexing of the container while lidding isapplied). Yet another function of the extension 50 can be to provide aspace which the deflectable flange 160 can occupy when it is deflectedanti-peripherally. Because the extension 50 and the peripheral flange120 are situated on opposite sides of the bend region 150, sufficientflexing of the bend region 150 (e.g., upon insertion of the article 100within the upper body 200 and insertion of the ram 300 behind thearticle), the spacer 140, or both, can cause the peripheral flange 120(and the spacer 140) to approach, or even contact, the extension 50, orto curl or deflect beneath the extension 50 between the periphery of thearticle and a sidewall of the body of the article (see, e.g., FIG. 6E).

In FIG. 1A, the peripheral flange 120 includes the (potentially sharp)peripheral edge 110 of the thermoplastic sheet(s) from which the articleis formed. It extends peripherally beyond the bend region 150, so thatit will impinge upon the inner surface 202 of the upper body 200 whenthe article is inserted into the cavity of the upper body 200, as shownin FIG. 1B. It extends from the elbow 130 to that peripheral edge 110and extends in a direction from the bend region 150 or the spacer 140,if present, by an offset angle defined by the elbow 130. The function ofthe peripheral flange 120 is to engage with (i.e., impinge upon or beimpinged upon by) the inner surface 202 of the upper body 200 when thearticle is inserted into the cavity of the upper body 200, therebycausing the deflectable flange 160 to deflect inwardly(anti-peripherally). In addition to displacing the peripheral edge 110of the sheet anti-peripherally and causing flexing or bending of thedeflectable flange 160 in the bend region 150 thereof, this deflectionalso positions the peripheral flange 120 to be further anti-peripherallydeflected when the ram 300 is inserted into the cavity behind thearticle 100. When the ram 300 is so inserted, it impinges upon theperipheral flange 120 and, upon further advancement of the ram into thecavity, causes both additional flexing or bending of the deflectableflange 160 in the bend region 150 thereof, and additionalanti-peripheral deflection of the peripheral edge 110.

The length (elbow-to-peripheral-edge) of the peripheral flange 120 isnot critical, but should be selected to facilitate engagement of the ram300 by the peripheral flange 120 and displacement of the peripheralflange 120 by the ram 300 as the ram advances within the interior of theupper body 200. Frequently, the length of the peripheral flange 120 isinfluenced, at least in part, by the ability to cut articles from amaterial in which the article is formed. The elbow 130 can function, inpart, to position the thermoplastic sheet at a location at which it canbe conveniently cut to free the shaped article from a precursor sheet.Because the peripheral edge 110 formed by such cutting is a source ofsharpness or roughness at the periphery of the article prior to ‘rollingover’ the deflectable flange 160, it can be beneficial to cut the sheetas near to the elbow 130 as possible (i.e., to make peripheral flange120 as small as possible) so as to reduce the bulk of thermoplasticmaterial that must be displaced in order to displace the sharp or roughperipheral edge 110 from the periphery of the article. As illustrated,for example, in FIG. 8H, a larger peripheral flange also reduces contact(and increases spacing) between the upper surface of a ram whichimpinges the deflectable flange, and therefore reduces heat transferfrom the ram to peripheral portions of the deflectable flange. Becausethe methods described herein depend upon heating those portions abovetheir glass transition temperature, deflecting them to a desiredconformation, and then cooling the portions below that temperature,larger peripheral flanges increase the heat input and/or time requiredfor such processing and are disfavored for that reason as well.

The elbow 130 is interposed between the bend region 150 and theperipheral flange 120, and its function is to connect and transferforces between them. That is, compressive forces applied to theperipheral flange 120 by impingement thereupon by the upper body 200 orthe ram 300 are translated through the elbow 130 (and the spacer 140, ifpresent) to torsional force applied to the bend region 150. Thistranslation of compressive force to torsional force ensures that thebend region 150, the spacer 140, or both flex when force is applied tothe peripheral flange 120. Thus, application of force to the peripheralflange 120 by the upper body 200 and/or ram 300 both deflects theperipheral edge 110 anti-peripherally (i.e., displacing the potentiallysharp edge away from the periphery of the article) and induces bendingof the bend region 150, the spacer 140, or both (i.e., yielding a smoothperiphery formed by flexed thermoplastic sheet at the periphery of thearticle), yielding an article which has a smooth periphery, even if thearticle was formed by a process that yields a sharp peripheral edge atan intermediate step. In effect, the elbow causes forces applied to theperipheral flange 120 to induce the deflectable flange 160 to “rollover” the periphery of the article, effectively “hiding” the sharp edgeof the thermoplastic sheet from materials at the periphery of thearticle.

A spacer 140 can be interposed between the bend region 150 and the elbow130. The spacer 140 can be discretely discernible from the bend region150 (e.g., a flat region distinct from a curved bend region 150) orsubstantially indistinguishable (e.g., a slightly curved region notreadily distinguished from the curvature of the bend region 150). Thedimensions of the extension region are not critical; it can range fromnon-existent (i.e., the bend region 150 commences at the elbow 130), toa fraction of a millimeter, to a few millimeters or longer. One functionof the spacer 140, if present, is to act as a ‘lever’ by which forceapplied at the elbow 130 (e.g., by impingement between the peripheralflange 120 and one or both of the upper body 200 and the ram 300) istransmitted to the bend region 150. Another function of the spacer 140,if present, can be to position the peripheral flange 120 suitably toengage one or both of the upper body 200 and the ram 300. Yet anotherfunction of the spacer 140, if present, is to increase the distance bywhich the potentially sharp peripheral edge 110 of the thermoplasticsheet can be displaced anti-peripherally from the periphery of thearticle upon flexing of the bend region 150. All else being equal, thelonger the spacer 140 is, the farther from the article's periphery thatpotentially sharp edge will be when the article is made as describedherein. A deflectable flange including the spacer 140, but lacking theelbow 130 and peripheral flange 120 can be used, as shown for example inFIGS. 8A-8D.

A longer spacer 140 facilitates formation of one or more portions of the“rolled edge” that is taller than other “rolled” portions of the edge,yielding a structure useful as a stacking lug (e.g., to facilitateselectable spacing between the rolled edges of adjacent nested, stackedarticles). In one embodiment, the size of the spacer and the compressiveforce applied to the spacer (i.e., the force transmitted to the spacerfrom the extension region, balanced by resistive force applied to thespacer on account of its impingement upon the ram) can cause the spacerto flex outwardly (i.e., peripherally away from the body of thearticle), forming a smooth bulge that, upon cooling, forms the outerperiphery of the article.

Regardless of whether the bend region 150, the spacer 140, or both arebent in the operations described herein, and further regardless ofwhether material that was originally part of the bend region 150, thespacer 140, or both ultimately form the outer periphery of the articlesdescribed herein, what is important is that that outer periphery be free(or, less favorably, substantially free) of sharp, pointed, rough, orabrasive edges that might damage thin plastic films, human tissues, orother fragile materials which might contact that outer periphery.

Thermoplastics

The methods and articles described herein can be performed and made withsubstantially any thermoplastic material. What is important is that thematerial be capable of being softened by heating and re-stiffened uponcooling, at least in the deflectable flange 160 described herein.Substantially all thermoplastics exhibit a characteristic temperatureabove which they soften and become flexible or workable and below whichthey become more rigid and retain their shape. Desirable thermoplasticsfor the articles and methods described herein retain their shape undernormal conditions of the anticipated end use of the container. It isalso desirable to use thermoplastics which can be softened underconditions that are readily attainable in a manufacturing environments.Examples of suitable thermoplastics include polyethylene (PE),polypropylene (PP), polyethylene terephthalate (PET), and polyvinylchloride (PVC). Other suitable thermoplastics are apparent to skilledworkers in this field, and substantially any of these can be used. Alsopotentially useful are flexible plastics having deformable materialssuch as metal foils bound to their surface.

The thermoplastic article includes a thermoplastic material, includingat at least the portions of the article at which the deflectable flange160 described herein is formed or present. The identity of thethermoplastic material is not critical, nor is the presence or absenceof non-thermoplastic materials. Where non-thermoplastic materials arepresent (e.g., in a thermoplastic sheet to which a metal foil or apaperboard layer is laminated), the rigidity imparted to the article bythe thermoplastic material in its non-softened, non-molten state ispreferably sufficient to define the conformation of the article, evenwhen the non-thermoplastic material is bent. The article can include oneor more peelable layers, for example as described in co-pending U.S.patent application Ser. No. 13/415,781. When one or more peelable layersis present, it is substantially unimportant whether those layers are“rolled over” at the peripheral edge of the shaped article (rather thanthe edges of the peelable layers peeling from the underlying substrate).Both for aesthetic reasons and to promote sealing, it can be preferablethat any peelable layers remain adhered. When peelable layers arepresent and adherence is to be promoted, the working temperature shouldbe selected both to be suitable for deflection of the deflectable flangeas described herein and for working the substrate and peelable layers ofthe shaped article without causing delamination of the peelable layers.

The Upper Body 200

The upper body 200 performs a number of functions. Overall, its functionis to contain the deflectable flange 160 described herein within acavity in the upper body 200 while heat is applied to one or moreportions of the bend region 150 thereof. This containment function canprevent non-desired deformation (or guide desired deformation) of thedeflectable flange 160 or portions of it during the periphery-smoothingoperations described herein. The shape of the interior cavity of theupper body 200 can also affect the shape of the deflectable flange as itbends, particularly as it is softened. By way of example, in FIG. 1B,the upper body 200 includes a cavity with an internal right angle intowhich a portion of the bend region 150 is forced; the right-angle shapeof this portion of the cavity will tend to cause the bend region 150 toconform to a right-angle shape, especially as the bend region 150softens. The heat source can be a part of the upper body 200, applied tothe upper body 200 for conduction of heat therethrough, for example. Theupper body 200 also impinges upon and is impinged upon the peripheralflange 120 of the deflectable flange 160 when it is inserted into thatcavity. When a ram 300 is used, the upper body 200 also serves toprevent the deflectable flange 160 from being forced out of the cavity,and it can also limit deflection of the bend region 150 when thedeflectable flange 160 is being compressed by the ram 300.

The materials from which the upper body is constructed are not critical,other than that they should be suitable to withstand the manufacturingconditions described herein. That is, they should not melt or degrade atthe temperatures used in the processing. A wide variety of metal,ceramic, stone, and polymeric materials can be used.

It is important that the shape of the upper body 200 be selected so thatimpingement between the interior of the cavity in the upper body 200 andthe peripheral flange 120 will occur when the article 100 describedherein is inserted into the cavity in the upper body. The upper body canhave a shape sufficient to simultaneously impinge multiple peripheralflanges 120 on an article, or to impinge upon most or all of a singleperipheral flange 120 that occurs upon an article (e.g., one whichoccurs about the entire peripheral edge of an article). As illustratedin FIG. 2, the upper body 200 can be formed of a solid block of materialthat covers an entire face of an article while impinging peripheralflange(s) 120 that occur on one or more portions of the article. Theupper body 200 depicted in FIG. 2, for example, is designed to impingeupon the single peripheral flange 120 that extends completely around theperiphery of an article having the shape of a rectangular tray-typecontainer having rounded corners.

The bend region 150 of the articles described herein will typically bewithin the cavity of the upper body 200 when heat is applied to thatbend region 150. For that reason, the upper body should be constructedin a way that facilitates application of such heat. The upper body 200can, for example, include a heat source (e.g., electrically operatedheating plates or rods) within it, applied to it, or fluidly connectedwith it. Alternatively, the upper body 200 can include one or more portsthrough which a heated fluid (e.g., a heated gas or liquid) can passfrom a source into the interior of the cavity therein. The methodselected to deliver heat to the bend region 150 (and/or other portionsof the peripheral flange, such as the spacer 140, the elbow 130, and theperipheral flange 120) is not critical, and any of a variety ofwell-known heat delivery methods and equipment can be used. If the upperbody 200 is able to conduct heat and is cooled, then heat that ispresent in the deflectable flange 160 during its shaping can flow to theupper body 200, and this heat flow can serve to cool and thereby stiffenthe deflectable flange 160 in its deflected position upon itscompression between the upper body 200 and the ram 300, for example.

As shown, for example in FIGS. 5 and 8, the deflectable flange can bedeflected using a ram 300 alone, with or without use of an upper body200. The upper body can be used both to partially deflect thedeflectable flange and to apply force to the article so as to impingethe deflectable flange thereof against the ram. When the upper body 200is not used, some alternate means of applying force to the article tocause impingement between the ram and the deflectable flange must beused. In FIG. 8D, for example, this alternate means is depicted simplyas object 403 (optionally coordinated with object 402). The orientationof the parts relative to gravity is not important, the “downward” force(open arrow in FIG. 8D) need only be directed so as to urge thedeflectable flange 160 against the ram 300 to cause impingement betweenthe two. It is also immaterial to which of the article and the ram (orboth) force is applied in order to cause such impingement. What isimportant is that impingement of the deflectable flange 160 against theram 300 (and/o the upper body 200, if used) induces deflection of theperipheral edge 110 of the deflectable flange to a position where it isnot readily accessible at the periphery of the article. Thus, in oneembodiment, the upper body 200 can be a simple flat plate which can beapplied against a flat portion (e.g., the extension 50 of thedeflectable flange 160 depicted in FIG. 8D) of the article to drive thedeflectable flange in the direction of, and ultimately against, the ram.

The Ram 300

The primary function of the ram 300 is to induce deflection in thedeflectable flange. The ram can be used with or without a correspondingupper body 200, but such an upper body can serve to contain and controlthe article as it is contacted with the ram. The method and mechanism(s)used to impart relative motion between the article and the ram are notcritical. When an upper body is employed, the ram is used to impingeupon and apply compressive force to the peripheral flange 120 of thedeflectable flange 160 when the article is disposed in the upper body200. This compressive force tends to drive the peripheral flange 120upwardly toward the bend region 150 and the extension 50, if present,and anti-peripherally, thereby moving the potentially sharp peripheraledge 110 of the thermoplastic sheet away from the periphery of thearticle so formed. Accordingly, the design of the ram 300 is notparticularly critical, so long as such compressive force is applied. Asillustrated in FIGS. 1C and 4, a ram 300 having an angled upper face 302will tend to direct the peripheral flange 120 in the direction alongthat angle as it compresses the peripheral flange 120. Thus, it can bebeneficial to shape the upper face 302 of the ram 300 in a conformationthat deflects or “pushes” the peripheral flange 120 and/or theperipheral edge 110 anti-peripherally as compression occurs.

Like the upper body 200, the materials from which the ram 300 is madeare not critical. Metals, ceramics, stones, and polymeric materialscapable of withstanding the temperatures and pressures of operation aresuitable and readily selectable by a skilled artisan. If the ram 300 isable to conduct heat and is cooled, then heat that is present in thedeflectable flange 160 during its shaping can flow to the ram 300, andthis heat flow can serve to cool and thereby stiffen the deflectableflange 160 in its deflected position upon its compression between theupper body 200 and the ram 300, for example. Heat can likewise beprovided by the ram 300 to one or more portions of the deflectableflange in conventional ways, such as by using a heated ram orincorporating a heating element into or onto the ram.

In an embodiment illustrated in FIG. 2, a single ram 300 can beconstructed to impinge upon substantially all peripheral flanges 120 ofan article simultaneously. The ram 300 depicted in FIG. 2, for example,is designed to impinge upon and apply compressive force to the singleperipheral flange 120 that extends completely around the periphery of anarticle having the shape of a rectangular tray-type container havingrounded corners.

In an alternative embodiment illustrated in FIG. 5, the deflectableflange 160 of an article is heated to softening and impacted against aram 300 in the absence of an upper body 200 of the type describedherein. The absence of an upper body 200 may lead to distortion ordeflection of softened portions of the deflectable flange 160, at leastif the other portions (e.g., the extension 50 or parts of the body 10 ofthe article 100 that are adjacent the deflectable flange 160 areinsufficiently rigid to prevent such distortion or deflection. However,if such rigidity is present, or if such distortion or deflection istolerable in the final product, the methods described herein can be usedwithout an upper body 200.

FIG. 5 also illustrates the significance of the length (measured fromthe elbow to the peripheral edge) of the peripheral flange. Theperipheral edge contacts the ram. Force imparted upon the peripheraledge by the face 302 of the ram induces deflection of the deflectableflange 160 toward the body 10 of the article 100. When the deflectableflange 160 includes a peripheral flange 120 that is offset from thespacer portion 140 by a ninety-degree elbow 130, as shown in FIGS. 5Aand 5B, the length of the peripheral flange will influence the degree ofdeflection of the deflectable flange. Comparing FIG. 5C (a deflectableflange in which the “length” of the peripheral flange is zero; i.e., adeflectable flange lacking a peripheral flange) with FIG. 5B, it can beseen that the presence of the peripheral flange induces greaterdeflection of the deflectable flange in the configuration shown.Moreover, looking to FIG. 5A, increasing the length of the peripheralflange increases the degree of deflection induced by the ram. Thus,although the elbow and peripheral flange are optionally not present,their presence enhances deflection and can enhance the “rolling” effectthat can be achieved.

FIG. 10 depicts an embodiment of the ram 300 described herein forrolling over the edge of a shaped article having a deflectable flange160. FIG. 10A depicts a ram 300 having at least two positions foraccepting articles 100 having deflectable flanges as described herein.The upper portion of the figure shows a position that bears an article100. Because it does not bear an article, the position partially shownin the lower right of the figure reveals the upper surface 302 uponwhich the article is borne when present. The position in which anarticle is borne in the figure has an identical upper surface 302, butit is obscured by the spacer 140 and peripheral flange 120 of thearticle 100 borne therein. This figure also illustrates how theextension 50 spaces the body 10 of the article away from the spacer andaway from the ram, providing space (visible through the clear materialthat forms the extension) into which the spacer and peripheral flangecan be deflected, bent, or curled.

FIGS. 10B and 10C show details of the upper surface 302 of the ram 300,including a curved portion (at approximately D in FIG. 10C) which willdeflect the peripheral edge 110 of the deflectable flange when urgedagainst it at a softened temperature. FIG. 10B is a close-up image ofthe upper surface, and FIG. 10C is a cross-sectional diagramillustrating the approximate shape of that upper surface. In operation,the ram is used by impinging the peripheral edge 110 of the deflectableflange against the upper surface 302 (from the ‘downward’ directionindicated by the open arrow in FIG. 10C) at a position anywhere betweenpositions B and D, and then applying further downward force to drive theperipheral portion of the deflectable flange further against the ram.This further force induces the peripheral edge to slide, scrape, or skipacross the upper surface and induces the deflectable flange to deflectinwardly (i.e., toward the body of the article which, in thisembodiment, is located closer to the E position than to any of A-D).When the deflectable flange is heated above its softening point (i.e.,glass transition temperatures), this deflection will be non-elastic andwill be reflected in the shape of the deflectable flange if it isthereafter cooled to a temperature below its softening point.

The curved portion of the upper surface 302 of the ram 300 betweenpositions C and E in FIG. 10C induces the softened portion of thedeflectable flange to roll or curve, and the degree of curvature inducedis controlled by the extent to which the deflectable flange is impingedagainst the ram. Thus, for example, only the peripheral-most portion ofthe deflectable flange might be deflected if the deflectable flange iscaused to impinge only slightly against the upper surface aftersoftening, the peripheral edge will be pointed approximately toward thebody if a softened portion of the deflectable flange is impinged to theextent of position D, and the peripheral edge of the deflectable flangewill be effectively “rolled over” (i.e., the plane of the deflectableflange at its peripheral edge extends to intersect the underside 161 ofthe deflectable flange) if a softened portion of the deflectable flangeis impingingly extended beyond position D (as shown in FIGS. 8G and 8K,for example). Depending on the material from which the deflectableflange is made, the deflectable flange can substantially retain itsshape as it cools in the ‘rolled over’ configuration (e.g., PET and PVCmaterials tend not to slump or droop when acted upon by gravity in asoftened state, while PE and PP materials can be bent substantially bygravity alone when softened). Even when this is not so, so long as theperipheral edge of a deflectable flange that droops or slumps does notexpose the peripheral edge at the periphery of the article, such bendingis acceptable (e.g., when the rolled-over edge is rolled oversufficiently that any drooping occurs in the interior space of theroll).

Sealing Films

An important advantage of articles having peripheries treated in themanner described herein is that such treatment renders the articlessuitable for sealing with thin plastic films. Sealing articles with thinplastic films is a well-known process, and many suitable films are known(e.g., thin monolayer or multilayer sheets made of materials such aspolyethylene or polyvinylidene chloride, optionally including polymerlayers which inhibit passage of moisture or certain gases). Articles canbe sealed with plastic films, for example, by completely enveloping thearticle in the film and sealing the film to itself. Alternatively,articles can be sealed by sealing a film about the periphery of aconcavity, compartment, or other orifice defined by an article and, ifdesired, thereafter trimming the portion(s) of the film beyond thatperiphery. All technologies for sealing articles with thin plastic filmsare believed to involve at least intermittent contact between peripheralareas of the article and the film used for sealing.

It is therefore beneficial for an article to be sealed with a thinplastic film to be free, or at least substantially free, of sharp,pointed, rough, jagged, or abrasive structures, at least at areas of thearticle which contact the film. It is particularly important that suchstructures be absent from the surface of the article which willnecessarily contact sealing films, and highly desirable that thesestructures are also absent from article surfaces which are likely tocontact sealing films, whether during the sealing process, or whetherduring further packaging, shipping, unpackaging, or retail display ofthe film-sealed article. Still more preferably, articles to be wrappedwith a thin film bear no such structures at surfaces at which there is asubstantial likelihood of contact between the surface and the filmduring any of these processes. Ideally, the articles bear no suchsurface at any position at which a film used for sealing mightreasonably be expected to contact the surface position during theseprocesses.

A wide variety of thin plastic films are known to be useful for sealingcontainers, and substantially any of these films can be used to seal theshaped articles described herein (or compartments thereof). Selection ofsealing films (and materials for making shaped articles compatible withsuch sealing films) is well known in the art, and substantially anyknown combination of materials can be adapted for use with the shapedarticles described herein. By way of example, when a sealing film is tobe removably sealed about a shaped article described herein (e.g., anoverwrap film that is sealed to itself but not to the wrapped article),the materials used to make the shaped article should be selected suchthat it will not fuse with the film under the sealing conditions to beused. By contrast, when a sealing film is to be substantiallypermanently sealed to a shaped article (e.g., about the perimeter of acompartment defined by the article), the material(s) used to make thearticle should be selected to facilitate formation of a substantiallypermanent seal under practical processing conditions. Similarly,combinations of sealing and container materials and operating conditionsthat yield containers sealed with material that is peelable therefromare known and can be used.

One highly desirable embodiment of the articles described herein is atray-shaped article that is made by thermoforming (and that thereforepossesses potentially sharp peripheral edges prior to the edge-rollingtreatment described herein) such that it possesses about its entireperiphery the deflectable flange described herein and for which theperipheral edge is deflected beneath the extension and behind the spacerand bend region of the deflectable flange, about the entire periphery ofthe tray, sufficiently that the peripheral edge cannot be touched by ahuman fingertip that is swiped along the gap between the deflectedperipheral flange and the body of the tray, even if that fingertip isswiped along this gap around the entire periphery of the tray. Such atray will bear no sharp, pointed, rough, jagged, or abrasive edge at anyposition that can reasonably be expected to contacted by a sealing film,regardless of whether OW, VSP, or MAP technology is used in the sealingprocess. A tray suitable for use with all of these sealing technologiesis highly desirable and believed to be unavailable prior to thedisclosure of the subject matter described herein.

Many plastic films used for sealing of articles are flexible and do notthermoset over the range of temperatures ordinarily employed duringsealing and subsequent handling. Flexible films that are sealed tosurfaces are sometimes difficult to remove in a single piece from thesealing surface. For example, a flexible film that is sealed about theflat periphery of a tray may tear or split when one portion of the filmis pulled away from the tray, potentially requiring a user to remove thefilm in multiple passes or many strips or pieces. Such difficulties maybe particularly acute in situations in which the sealing surface isbroad, such as in a VSP-sealed package in which a sealing film may beadhered to or fused with a relatively large area of a tray on which anitem has been sealed between the film and the tray. The technologydescribed herein can be used to reduce or overcome this difficulty asfollows.

The shaped articles described herein (e.g., a tray-shaped article havinga smooth periphery) can be sealed with a thermosettable (i.e.,thermoformable) film to yield an article in which the thermoformablesealing film is heated above its glass transition temperature to softenit and applied against the smooth periphery of the shaped article. Athermoformable film that is heated above the glass transitiontemperature of the material of which it is made and thereafter cooledbelow that temperature will retain whatever conformation the film has(e.g., a conformation imposed upon it) when the temperature falls belowits glass transition temperature. Thus, if a thermoplastic film isformed “around” (i.e., extending more than about 90 degrees about) thesmooth outer periphery of an article described herein, the film will beheld to the article not only by whatever attraction or adhesion mayexist between the film and the article surface, but also by mechanicalforces (i.e., the film's resistance to deflection about the smooth outerperiphery), forming a structure analogous to a “snap off” lid.

Even though softened thin plastic films can be extremely delicate (e.g.,liable to be damaged by sharp, pointed, rough, jagged, or abrasivesurfaces), the smooth periphery of the shaped articles described hereinpermits even such delicate films to be applied thereto. In one example,a shaped article in the form of a tray having a smooth periphery can beVSP-sealed to encase an article between a softened thermoplastic sealingfilm and the tray, with little or no gas included within the sealedportion. Furthermore, the smooth periphery of the articles describedherein permits a softened film to be drawn, pressed, or formed aroundthe smooth periphery—that is, contacting not only the top portion of theperiphery (i.e., analogous to the extension 50 of the article edgedepicted in FIG. 9B), but around the bend region 150 of the deflectableflange, and along the spacer 140 and any bent or rounded portionsthereof (such as to or around the rounded underside 145 of the spacerdepicted in FIG. 9B) and thereafter set by reducing the temperature ofthe sealing film below its glass transition temperature. Such a sealwill form a relatively rigid “lid” and, even if the film is not adheredor fused to the shaped article where the film intersects the article,frictional forces or the shape of the “lid” (e.g., turned about therounded underside 145 of the spacer depicted in FIG. 9B, such that the“lid” must be stretched or expanded to disengage it from the rolled overperipheral flange 160) can hold the sealing film in place on thearticle. Furthermore, because softened thermosettable film can besubstantially thicker, therefore stronger, and/or more rigid than thinflexible sealing films, a thermosettable sealing film can form a seal or“lid” that can tend to be more likely removable in a single piece.

In one embodiment of the shaped articles described herein, for example,the article is a tray having a food item placed thereon, with athermosettable film draped across the food item and the periphery of thetray while the film is in a softened state; gas between the film and thetray is withdrawn to form a VSP-type seal (with the film closely opposedagainst the food item and the tray surface upon which the food itemrests); and the film is draped around (from the top, to or around, thebottom of the periphery), optionally sealed or fused to the tray,trimmed about the bottom of the tray periphery, and cooled. In thefinished tray, the “lid” formed upon cooling of the film must be“snapped off” the tray by stretching the edge of the lid around theperiphery of the tray, but once this operation is performed, the entirelid can be removed from the tray in a single piece.

In another embodiment, a shaped article described herein is sealed(after its smooth outer periphery has been formed) using athermoformable plastic film that is extended across a compartmentdefined by the article and at least about 90 degrees about opposedsmooth peripheral sides of the article (i.e., opposite ends of a roundedrectangular tray). The film is heated above its glass transitiontemperature and cooled below that temperature while extended about theopposed smooth peripheral sides. If desired, a vacuum or modifiedatmosphere can be applied to the compartment during such sealing. Theresulting article has a thermoset film cover that must be stretched (or“snapped”) around at least one peripheral side of the article in orderto remove the film from the article (in addition to any other seal thatmay exist between the film and the article).

The shaped article described herein can be used in ways which arebelieved to be not possible using previously-known trays. Typically,others have used containers especially designed and made for each of thevarious sealing technologies described herein (e.g., OW, VSP, and MAPtechnologies) for sealing containers with thin plastic films. That is,food trays designed for OW-sealing have been generally consideredunsuitable for VSP- and MAP-wrapping (e.g., owing to the lack ofsurfaces suitable for sealing in VSP- and/or MAP-technologies).Similarly, the sharp edges of many containers designed for use with VSP-and MAP-sealing technologies render those containers unsuitable foroverwrapping with fragile polymer films. The shaped articles describedherein can be used to make shaped articles that can suitably be used ascontainers for sealing by any of OW, VSP and MAP technologies. Becausethe shaped articles are thermoformed, container surfaces suitable forVSP- and/or MAP-sealing can be included in the shape of the articles.Using the methods described herein, any edges of a shaped article whichmight provide a risk of tearing sealing films (or, alternatively, alledges of the shaped article) can be made to have a smooth conformation,such as by forming a rolled-over edge or by smoothing the shape of themold used for thermoforming the precursor article. Thus, unlikepreviously-known trays, the shaped articles described herein can be usedwith substantially any film-sealing technology.

Other advantageous uses of the shaped articles described herein relateto the smoothness of their edges. The articles can be used insubstantially any environment in which it is desirable or necessary thata solid object exhibit smooth edges. By way of example, instruments usedin surgical procedures are typically packaged in openable containers (topermit reuse and sterilization between uses) that are opened bypersonnel wearing easily-torn surgical gloves during medical surgeryprocedures. Thermoformed articles (e.g., so-called “clam-shell” typesnap-open packages of known design) can be made as described herein,with those articles being initially made having a deflectable flangewherever they are cut from the web of thermoformed material, andthereafter rolling over that deflectable flange to yield the smooth edgedescribed herein. Articles made in this manner will present smooth edgesto users, reducing the likelihood that surgical gloves will be torn byopening such packages during surgery procedures. Similarly, thermoformedpackages of known design that are employed to facilitate handling, toinhibit theft, or to achieve other ends can be adapted (e.g., byincluding a deflectable flange in their design and rolling it over) totake advantage of the edge-smoothing technology described herein.

System for Forming Articles

As described above, precursors of the shaped articles described hereincan be formed by standard thermoforming methods, using standardthermoforming equipment. To do so, a thermoforming mold is used to makea precursor article by imposing upon a thermoplastic sheet the desiredconformation of the finished article, except that the deflectable flangedescribed herein is included at the peripheral edge(s) at which thesmooth periphery is to be formed. Upon cutting the precursor articlefrom the web of thermoplastic sheet, the edge-smoothing operationsdescribed herein can be performed by impinging the deflectable flangeupon the ram (optionally with the aid of an upper body).

Newly-thermoformed precursor articles will tend to emerge from thethermoformer at a temperature close to (but below) the glass transitiontemperature of the thermoplastic. Impinging the deflectable flange andthe ram shortly after removing the precursor article from thethermoformer can reduce the quantity of heat energy which must besupplied to one or more portions of the deflectable flange in order toachieve the desired deflection (or “rolled over” edge effect) of thedeflectable flange described herein. For this reason, it can bedesirable to combine the thermoformer, the ram, and an impingementmechanism into a single system or a single piece of equipment. Such asystem or piece of equipment should include i) a thermoformer modulecapable of forming the precursor article; ii) a cutter for cutting theprecursor article from a thermoplastic sheet or roll from which it wasformed; iii) the ram; and iv) a mechanism for positioning the precursorarticle against the ram (i.e., so that the deflectable flange portionsline up with the corresponding ram portions) and impinging the precursorarticle and the ram together. The heat required during the deflectableflange-deflection operations described herein can be provided by theram, by the cutter (e.g., using a heated cutting blade to heat theperipheral edge and an adjacent peripheral portion of the deflectableflange above the softening temperature of the thermoplastic), by aseparate heater (e.g., a radiant heating element disposed in closeopposition to the ram when it is engaged against the deflectableflange), or by a combination of these. The precise selection,orientation, order, and construction of these pieces of equipment arenot critical and can be selected by a skilled artisan in light of therequirements and processing steps described herein. The system orequipment can also include the plug described herein for insertionwithin a void in the precursor article prior to impingement of thedeflectable flange against the ram.

EXAMPLE

The subject matter of this disclosure is now described with reference tothe following Examples. These Examples are provided for the purpose ofillustration only, and the subject matter is not limited to theseExamples, but rather encompasses all variations which are evident as aresult of the teaching provided herein.

Example 1

FIGS. 6A and 6B illustrate a thermoplastic tray which was thermoformedfrom a flat sheet of thermoplastic material and then cut from the sheet.The sharp edge formed by the cutting process is shown in each of thesefigures, with a finger touching the sharp edge. After the smoothingprocess described herein was performed on these trays, the appearance ofthe trays was approximately that shown in FIG. 3, in which the sharpedge has been “rolled over” such that it faces the body of the tray anda smooth portion, formed by flexing at least the bend region of thedeflectable flange and heating and cooling it to yield a smooth outerperiphery to the tray which will not impact either upon a thin plasticfilm attached to the rim of the tray or upon a thin plastic film whichis snugly wrapped about the entirety of the tray.

Example 2

This example is provided for the sake of explaining formation andsealing of a shaped article as described herein. In this example,formation, filling, and sealing of a container containing a cut of freshfish is described.

A shaped article for receiving the fish is formed by traditionalthermoforming methods. A thermoformable material (e.g., PET) in sheetform is heated above its glass transition temperature and urged againsta mold using traditional thermoforming techniques (using either a maleor female mold, with or without the application of positive and/ornegative pressure to urge portions of the sheet against portions of themold). Such thermoforming yields a tray-shaped container having arounded rectangular shape overall and including a concave interiorportion for receiving the cut of fish. The rounded rectangular overallshape of the container is defined by a deflectable flange that surroundsthe interior portion about the entire perimeter of that interiorportion. The deflectable flange has the configuration shown in FIG. 1A,and the tray has the approximate shape of the tray shown in FIG. 6D uponcutting the thermoformed tray from the sheet at peripheral edge 110 ofthe deflectable flange 160. The die used to cut the tray from the sheetis heated so that the peripheral edge of the tray is at or near itsglass transition temperature.

A plug having a shape that substantially fills the interior portion ofthe tray at the portions adjacent the extension 50 of the deflectableflange 160 is inserted into the interior portion (approximately as shownin FIG. 8Dii). The plug-filled tray is then inserted into a ram 300(approximately as shown in the upper position in FIG. 10A, except thatno plug is present in FIG. 10A), so that the peripheral edge 110, thespacer 140, or both contact the upper surface 302 of the ram 300 atsubstantially all portions of the deflectable flange. Downward pressure(referring to FIG. 10A, the force being applied downwardly from the topof the image) is applied to the extension 50 of the deflectable flange160 about the entire periphery of the interior, driving the spacer 140and/or peripheral edge 110 portions of the deflectable flange 160against the ram. The deflectable flange is driven against the ram to aposition analogous to that shown in cross-section in FIG. 8H, and theparts are held in this position for a period of time sufficient for atleast the portion of the deflectable flange indicated by “B” in FIG. 8 Jto attain a temperature above its glass transition temperature by virtueof heat conducted or radiated thereto from the ram. The deflectableflange is thereafter urged (by the force applied to the extension 50)further against the ram so that the peripheral edge 110 slides, scrapes,or skips across the inner surface 302 of the ram 300 and the deflectableflange advances to approximately the position shown in FIG. 8J. Ifdesired, the deflectable flange can be further advanced to the positionshown in FIG. 8K, optionally upon pausing to permit additional portionsof the deflectable flange to achieve a temperature above its glasstransition point. Also, if desired, a coolant such as ambient air can beinjected (e.g. at the position occupied by element 120 in FIG. 8K) toreduce the temperature of the deflectable flange at the injection point,in order to prevent further irreversible deflection of such portion. Thedeflectable flange is urged against the ram sufficiently that theperipheral edge is not readily accessible to films or other materialspresent at the periphery of the tray.

The force urging the deflectable flange against the ram is discontinued,and the article is removed from contact with the ram, whereby thematerial of the deflectable flange cools below its glass transitiontemperature and retains its shape in the absence of applied force. Atthis point, a shaped article in the shape of the desired tray has beenformed, the tray having a smooth periphery. The tray can be usedimmediately for packaging the cut of fish or, more typically, it can bestacked with other such trays and shipped to a fish processor.

Whether the tray is used immediately after formation or retrieved byde-nesting the tray from a stack of trays, the cut of fish can now bedeposited within the interior compartment of the tray, together with anyother materials (e.g., sauce, an absorbent pad, vegetable, orseasonings) to be packaged therewith in preparation for sealing. Any ofa number of known sealing technologies can be used to seal the containerand the fish.

The tray can simply be over-wrapped with a thin plastic film (the filmextending across the opening of the compartment between extensions 50 onopposite sides of the compartment, around smoothly-bent bend region 150and/or spacer 140 of the deflectable flange 160), and the terminus ofthe film can be sealed to a portion of the film overlaying the tray, forexample by application of a heated pad against the terminus and theportion, followed by heat-shrinking of the film to yield a visuallypleasing taut film surface. Because the tray has no sharp or rough edgesat its periphery, the overwrapped film is not torn during sealing, nordo such edges tear, snag, or abrade other sealed packages duringshipping. The over-wrapped, fish-containing container can be packaged(e.g., in a box with other such containers or in a plastic bagcontaining both a selected gas or liquid phase and other suchcontainers), and shipped to a wholesaler, retailer, or customer.

Rather than sealing the package using an over-wrap that is sealed toitself, the container can be sealed after filling with a film that doesnot envelop the tray, but instead seals the compartment at the extension50 about the periphery of the compartment. Such a seal can be generatedby simply sealing a film (using any one or combination of heat,pressure, and an adhesive) to the extension 50 and, preferably, trimmingthe film about the periphery of the seal (e.g., by trimming the film atapproximately the peripheral extent of the container). If desired, anyfree ends of the film seal can be shrunk using heat. Prior to sealing, avacuum can be applied to withdraw gases from the interior of thecompartment and to draw the film against the contents of thecompartment, and a selected gas or gas mixture can optionally beinjected prior to sealing.

Example 3

Rolled Edge MAP Tray Having a Peelable Surface

An embodiment of the thermoplastic articles described herein has provento be of particular utility and is specifically described in thisexample. This embodiment is an article having the shape of any of theindustry-standard tray-shaped containers colloquially referred to as“MAP trays” among skilled artisans in this field. Such trays have aconcave interior space for holding or containing an article (e.g., a cutof fish, poultry, or other meat, a collection of plant parts such asvegetables, mushrooms, or fruits such as cherries). A rim completelysurrounds the concave interior space, such that when the MAP tray isplaced on a horizontal surface (MAP trays tend to have a flat bottom tofacilitate stable placement upon horizontal or inclined surfaces),materials within the concave interior space generally do not flow,spill, or roll over the rim and thereby exit the concave interior space.Atop the rim and extending (usually completely) around the opening ofthe concave interior space is a planar sealing surface. In use, a thinplastic film (i.e., a lidding film) is draped or stretched across theopening of the concave interior space and then sealed (e.g., using heat,adhesive, or mechanical impact force) to the planar sealing surface ofthe tray. As noted above, sharp or rough peripheral edges of thematerial from which a MAP tray is made can cut, snag, abrade, or tearsuch lidding films (e.g., film being applied to a first MAP tray or filmattached to a second MAP tray, such as one being shipped together withthe first).

In the embodiment described in this example, a MAP tray is made bygenerating (e.g., by thermoforming) a precursor tray which has theconformation of the desired bottom, rim, and concave interior space ofthe desired MAP tray, and which also bears the deflectable flangedescribed herein atop the rim at all positions at which a planar sealingsurface is desired. Typically, MAP trays have a planar sealing surfacecompletely surrounding the opening of the concave interior space; theprecursor tray corresponding to such a MAP tray would bear thedeflectable flange completely around the perimeter of the opening of theconcave interior space. The deflectable flange of the precursor tray isthereafter bent, deflected, or rolled, as disclosed herein to yield thesmooth edge described herein. The extension of the deflectable flange isselected to have a size sufficient to yield the a planar sealing surfacehaving a desired dimension (e.g., a width of at least ¼ inch about theentire periphery, measured in the radial direction from the center ofthe MAP tray) following edge-smoothing of the precursor tray.

Importantly, in the embodiment described in this example, thethermoformable sheet used to form the precursor tray has a peelablelayer (i.e., a “liner sheet”) attached to it, such as along one face ofthe thermoformable sheet. The liner sheet can be attached to thethermoformable sheet prior to forming the precursor tray (e.g., bylaminating the two sheets prior to thermoforming), during formation ofthe precursor tray (e.g., by simultaneously urging the two sheetstogether while thermoforming one or both of them), or (less preferably)after the precursor tray has been formed. The liner sheet preferablycovers an entire face of the thermoformable sheet, such as the facewhich defines the concave interior portion of the precursor tray.Multiple liner sheets can be adhered to the thermoformable sheet, suchas adjacent one another, overlapping, or (more preferably) in a“stacked” conformation in which a first liner sheet covers the face ofthe thermoformable sheet, a second liner sheet covers the exposed face(i.e., opposite the face bound to the thermoformable sheet) of the firstliner sheet, and, optionally, additional liner sheets cover the exposedface of a previous liner sheet.

In another embodiment, one or more liner sheets are attached to thethermoformable sheet after it has been thermoformed to yield theprecursor tray. In this embodiment, a sheet material intended to beattached to the tray is heated to at least its softening point, appliedagainst a surface of the tray (e.g., the face of a MAP tray whichdefines its concavity and surrounding rim) and any gas or other fluidbetween the tray surface and the liner sheet is withdrawn (e.g., byapplication of a vacuum to the space between the tray and liner sheet).The softened liner sheet is thereby drawn against the face of the trayand can adhere to it (by virtue of the nature of the opposed polymersurfaces or by an adhesive applied to one or both opposed surfaces).Upon cooling, the liner sheet has the conformation of, and adheres to,the face of the tray against which it was applied and drawn. If theliner sheet extends beyond the periphery of the tray, then it can betrimmed in any known manner (e.g., by “punching” out the portion of theliner adhered to the tray from a larger sheet of liner material using atray-periphery-shaped die, or by running a blade along the edges of thetray). Also, the trimming operation can leave a tab of liner sheetmaterial that is not adhered to the tray (e.g., to facilitate peeling ofthe liner from the tray). This operation can be repeated twice or moretimes to add additional liner sheets to the tray. When multiple linersheets are added to the tray, they can overlap completely, partially, ornot at all (i.e., they can be applied to different portions of thetray). In a useful embodiment, multiple liner sheets are applied to atray in this manner, and each of the multiple liners completely coversthe same face of the tray, except at tabs corresponding to each sheet,the tabs being cut in such manner that the tabs are distinguishable fromone another, so as to permit peeling of a desired liner using thecorresponding tab. For example, a rounded rectangular tray having threeliners may have a tab for the lowermost (i.e., adjacent thethermoformable sheet) liner sheet at the corner of the tray, a tab forthe uppermost liner sheet at the midpoint of the longer side of thetray, and a tab for the intermediate liner sheet at the midpoint of theshorter side of the tray.

For the rolled-edge trays (and, more broadly, for rolled-edge shapedarticles) described herein, the liner sheet can be added before or afterperforming the edge-rolling operation described herein upon thethermoformable shaped article. That is, one or more liner sheets can beapplied to a face of the shaped article (including, if desired, adeflectable flange portion thereof) prior to edge-rolling and thedeflectable flange (including an added liner) can thereafter be bent androlled as described herein. Alternatively, a shaped article can bethermoformed (e.g., including the deflectable flange described herein),its edge can be rolled, and liners added to one or more faces thereofafter the edge-rolling operation has been completed. In one embodiment,for example, a thermoformable sheet is formed, by a thermoformingprocess, into individual trays which have the deflectable flangedescribed herein completely about their periphery. The formed trays canbe subjected to the edge-rolling process to yield stackable trays havingsmooth peripheral edges. The smooth-edged trays can be stacked andstored. At a later time, a stack of trays can be denested to yieldindividual smooth-edged trays, and the individual trays can be fed intoa VSP work station to which a continuous roll of liner sheet material isfed. At the work station, the liner sheet material is softened, drawninto and against the interior portions of the smooth-edged trays bywithdrawing gas from between the softened liner material and the formedtrays. The liner material is permitted to cool, yielding a smooth-edgedtray having a portion of the continuous sheet of liner material bound toits inner surface. After being drawn against the tray surface (i.e.,during that operation or after cooling), the liner sheet material can becut around the perimeter of the tray (optionally leaving a ‘loose’ pieceof liner material unbound to the tray, to act as a tab for later peelingof the liner) to yield an individual smooth-edged tray having a linersheet adhered thereto. The operation can be repeated as many times asdesired to add additional liner sheets to the tray.

The equipment and methods used to add liner sheets to the surface of apre-formed tray are not critical. Substantially any equipment andmethods capable of softening a liner sheet, opposing it against asurface of the pre-formed tray, and withdrawing gas or other fluidbetween the tray and the liner sheet can be employed. For example, astandard VSP workstation includes facilities for holding a pre-formedtray in a fixed position, softening a polymer sheet at a position nearthe tray, applying the softened polymer sheet against a face of thepreformed tray (e.g., against the upper rim surface of a tray having arim surrounding its concave interior), and withdrawing gas from thespace defined by the tray, the softened sheet, and their intersection.In a standard VSP workstation, this arrangement is typically used tosoften a sheet of lidding material, apply it against a tray, withdrawgas from the space between the lidding and the tray to bring the liddingflush against the surface of the tray and any materials carried on or inthe tray, and to seal the lidding to the tray. The same equipment setupcan be used to add a liner (instead of lidding) to a tray, although thesealing equipment is unnecessary (but can be used if desired). In thissetup, the tray will be empty (will not carry materials within or onit), so the softened liner sheet will be drawn flush against thesurface(s) of the tray when gas is withdrawn. Careful selection of traymaterial, liner sheet material, and (if necessary) barrier compositionwill yield a tray in which a liner that has been applied against thetray can be peeled therefrom when desired.

The material from which the liner sheet is made is not critical, but itis preferably a flexible plastic material. It is not necessary that theliner sheet be made of a thermoformable plastic, but it can be. Theliner sheet can also be a non-thermoformable plastic that exhibitssufficient flexibility to conform to the shape of the thermoformablesheet. The liner sheet can be made from the same material as thethermoformable sheet or a different material. By way of example, arelatively thick thermoformable sheet of PET can be used as a substrateand a relatively thin sheet of PE can be adhered to a face of the PETsheet (after or, preferably, before thermoforming the PET sheet to makethe shaped article). Because PE and PET exhibit similar shrink rates,temperature-influenced delamination of the two sheets should be limited.If the PE sheet is attached to the face of a PET sheet that defines aconcavity (e.g., the interior portion of a MAP tray or a VSP tray), thenit may be possible to peel the PE and PET sheets apart withoutdischarging the contents of the concavity from the PE liner sheet.Furthermore, if a lidding is attached to the liner sheet about itsperiphery, then it may be possible to detach the liner from the PETsubstrate sheet without losing materials sealed between the liner andlidding sheets.

FIG. 11 depicts a cross-section of a portion of a tray as describedherein. The tray is formed from a relatively thick, thermoformablesubstrate sheet 101 (e.g., a thick PET sheet) and a relatively thinliner sheet 500 (e.g., a thin PE sheet) adheres to one face of thesubstrate sheet 101. In FIG. 11A, the deflectable flange 160 at oneperiphery of the tray is shown, with the peripheral edge 110 of theadhered sheets displaced away from the body of the article (portionsbeyond “//” are not shown) by the extension 50 portion of thedeflectable flange 160. FIG. 11A thus represents how the periphery ofthis tray would appear after thermoforming the substrate sheet 101 andattaching the liner sheet 500 against one face of it (whether before,during, or after thermoforming), and prior to rolling the peripheraledge 110 as described herein. FIG. 11B depicts the same portion of thetray after such edge-rolling. In FIG. 11B, the substrate sheet 101 hasbeen rolled over sufficiently that its peripheral edge 111 points backtoward the body of the article. The liner sheet 500 remains againstflush against the surface of the substrate sheet 101 at all portionsother than near its peripheral edge 501; there, the liner sheet 500 haspeeled or curled away from the peripheral edge 111 of the substratesheet 101. Such peeling or curling can result, for example, fromfriction between the ram and the liner sheet 500 during the edge-rollingoperation, or peeling/curling can be deliberately initiated thereafter,such as by scratching the peripheral edge 501 of the liner sheet 500away from the peripheral edge 111 of the substrate sheet 101 using afingernail, tool, or frictional processing step. Although having apartially-peeled peripheral edge 501 can detract from the appearance ofthe liner sheet 500 or the article, the partially-peeled edgefacilitates further peeling of the liner sheet from the article. FIG.11C illustrates that a lidding 600 can be applied to (e.g., lain upon,adhered to by static charge or adhesive, or sealed or bonded together byapplication of pressure and/or heat) the liner sheet 500, such as at theextension region 50 that extends about the periphery of a MAP or VSPtray. If the lidding 600 is attached to the liner sheet 500, rather thanto the substrate sheet 101, then the lidding 600 and liner sheet 500 canbe separated from the substrate sheet 101, optionally without severingthe attachment between the lidding 600 and liner sheet 500. If theshaped article has the conformation of a MAP tray with a liner sheet 500lining its concavity and sealing surface (i.e., a face of the extension50) and a lidding 600 is sealed to the liner sheet 500 at the sealingsurface completely around the periphery of the concavity, for example,then liner and lidding (and any contents sealed between them) can bepeeled from the rest of the MAP tray.

The precursor tray, with one or more liner sheets peelably attachedthereto, can then be subjected to the edge-smoothing process describedherein, wherein the deflectable flange is bent, deflected, or curled toyield a smooth peripheral edge to the finished MAP tray. Because thefinished MAP tray has a peelable liner attached to the thermoformablesheet, that liner can be peeled therefrom. Lidding material can beattached to the liner or to the thermoformable sheet, or can overwrapthe finished MAP tray. In one embodiment, the lidding is bound to theliner about the entire periphery of the sealing surface (therebydefining a compartment between the liner and the lidding) sufficientlyresiliently that the liner can be peeled from the thermoformable sheetwithout breaching the compartment. In this embodiment, the liner, thelidding, and anything contained within the compartment can be separatedfrom the MAP-tray-shaped thermoformable sheet (which can recycled, forexample) prior to accessing the contents of the compartment.Alternatively, the contents of the compartment can be accessed prior topeeling the liner from the MAP-tray-shaped thermoformable sheet, and theliner (and any remaining lidding) can be peeled therefrom afterwards.

If the liner completely covers a face of the thermoformable sheet priorto forming the precursor tray, it is possible that the liner may becomedetached from all or part of the peripheral edge during shaping of theprecursor tray. Similarly, even if the liner remains peelably attachedto the entire face of the thermoformable sheet after the precursor trayhas been formed, the liner may become detached from all or part of theperipheral edge during the edge-smoothing process described herein. Suchdetachment (delamination) can be undesirable (e.g., if the liner isintended to remain visually undetectable) and, if so, can be reduced orprevented by increasing the strength of binding of the liner to thethermoformable sheet, by increasing the pliability or thermoplasticstretching capacity of the liner, by reducing the ‘sharpness’ (i.e.,radius of curvature) of deflections made to form the precursor tray, byother methods known to skilled artisans in this field, or by acombination of these. On the other hand, partial delamination of theliner from the thermoplastic sheet, especially at its peripheral edgescan be desirable (e.g., to yield a free, grippable portion of the linerthat can be used to further peel the liner from the thermoplastic sheetwhen a user so desires). Such peeling can be enhanced or induced insimilar ways—e.g., by decreasing the strength of binding of the liner tothe thermoformable sheet, by decreasing the pliability or thermoplasticstretching capacity of the liner, by increasing the ‘sharpness’ (i.e.,radius of curvature) of deflections made to form the precursor tray, byrubbing or abrading the peripheral edge of the MAP tray, by othermethods known to skilled artisans in this field, or by a combination ofthese.

Example 4

Subject Matter Copied from U.S. patent application Ser. No. 13/415,781

As noted above, U.S. patent application Ser. No. 13/415,781 (now issuedas U.S. Pat. No. 9,302,842), which was co-pending with parent U.S.provisional patent application No. 62/212,367, was incorporated hereinby reference. In order to eliminate any doubt about whether the presentdisclosure explicitly contains any subject matter that might be properlyconsidered “essential material” as defined in 37 CFR 1.57(d), thefollowing portions of application Ser. No. 13/415,781 are incorporatedin this example verbatim. In the following incorporated subject matter,it should be understood that the “liner(s)” referred to in theincorporated subject matter is analogous to the “peelable layer(s)”referred to previously in this disclosure; that the “lidding” or“lidstock” referred to in the incorporated subject matter is analogousto the “lidding” referred to previously in this disclosure; and that the“substrate” referred to in the incorporated subject matter is analogousto the “shaped article” or “shaped thermoplastic article” referred topreviously in this disclosure. Other analogies between the incorporatedsubject matter and the subject matter referred to previously in thisdisclosure are believed to be apparent from the respect contexts.

The following text is incorporated in this example verbatim fromapplication Ser. No. 13/415,781:

This disclosure relates to containers which include at least onethermoformable component and which are made by layering at least onepolymeric sheet against a surface of a substrate. The sheet bounds areservoir or compartment within which liquid or another material can besequestered from the outside of the reservoir or compartment. Thereservoir or compartment can be bounded by the substrate, such that amaterial within the compartment or reservoir contacts the substrate, orit can be bounded by a second (optionally perforated) sheet such thatmaterial within the compartment is contained between the first andsecond sheets. The sheets can be peelably adhered or adhesed to thesurface of the substrate, to one another, or to both, such that thecontainer can be partially or wholly disassembled. In an importantembodiment, sheets which bound the reservoir or compartment can beseparated from the substrate without breaching the reservoir orcompartment.

Thermoformable Polymer Sheets

Each of the substrate and liner sheets described herein can be athermoformable polymer sheet. The identity and composition ofthermoformable polymer sheets used in the articles and methods describedherein are not critical. A skilled artisan will recognize thatsubstantially any thermoformable polymeric material can be used.Examples of suitable thermoformable polymeric materials includepolyethylene terephthalates, polyesters, polyethylenes (e.g., highdensity polyethylenes and high molecular weight polyethylenes),polypropylenes, polyvinylchlorides, polystyrenes, nylons, copolymers ofthese, and combinations of these. Plant-based polymers, such aspolylactates (also known as “lactic acid polymers” and PLAs) can also beused. Polymers used for contacting foods should, of course, be selectedfor compatibility.

Examples of suitable thermoformable polymeric materials for use assubstrates include polyethylene terephthalates (e.g., RPET, amorphousPET, and PETG), polyesters, polyethylenes (e.g., high densitypolyethylenes and high molecular weight polyethylenes), polypropylenes,polyvinylchlorides, polystyrenes, nylons, copolymers of these, andcombinations of these. Plant-based polymers, such as polylactates (alsoknown as “lactic acid polymers” and PLAs) can also be used.

A skilled artisan can select a thermoformable polymeric material, orcombinations of such materials, suitable for use in substantially anyapplication by considering such properties as the shrink rate,crystallinity, heat deflection temperature, tear strength, draw ratio,thickness, rigidity, melt temperature, thermal conductivity, and polymerbackbone orientation of the materials. Selection of materials can alsobe guided by properties that do not necessarily directly impact thethermoformability of the materials, such as cost, color, opacity,recycled material content, environmental impact, surface energy,chemical resistance, and surface sheen of the materials.

In selecting appropriate materials, an artisan should consider at leasttwo sets of conditions: the environmental conditions to which thefinished, shaped article will be subjected and the conditions that thematerials will experience during the thermoforming process. Materialsshould be selected so as to exhibit the desired color, shape, strength,rigidity, and peelability, for example, once the materials have beenshaped in the thermoforming process into their final, desired form. Thematerials should also be selected, together with the thermoformingconditions, so as to allow assembly and shaping of the materials intotheir final, desired form using thermoforming conditions available tothe artisan.

For deep-walled containers (i.e., containers for which substantialstretching of the planar substrate or liner stock materials would berequired upon forming of the container shape), a substrate blank molded,folded, or otherwise formed to have the approximately the finalconformation of the container can be used to reduce the risk ofrupturing the substrate on account of over-stretching. For example, if ametal foil substrate is used, it can be folded and compressed from aflat sheet of foil to form a blank having the approximate shape of thefinal container prior to applying a polymeric liner sheet thereto. Underconditions at which the liner sheet can be thermoformed, the final shapeof the container can be achieved by thermoforming the liner sheetagainst and re-shaping the blank in the thermoforming press.

For containers intended to contain foodstuffs (especially for humanconsumption), special consideration should be given to the choice ofsubstrate materials. If the substrate material contains, or potentiallycontains (e.g., for recycled substrate materials), any substanceinjurious to health, the substrate should be used only in conjunctionwith a liner sheet (and/or barrier sheets or compositions interposedbetween the substrate sheet and the liner sheet) sufficient to reduceforeseeable migration of the substance from the substrate to thecompartment under the conditions of anticipated use. Selection ofappropriate materials is within the ken of the skilled artisan in thisfield.

The Substrate

The identity and composition of the substrate is not critical. A skilledartisan will recognize that substantially any formable material can beused, such as metals and thermoformable polymers (which are preferredsubstrates). The substrate sheet described herein need not be thicker,more rigid, or more opaque than any other sheet used to make thearticles described herein. However, in many embodiments, it is desirablethat the substrate contribute the majority of the rigidity, strength,and shape of the article, with other components contributing relativelyless of these characteristics.

For example, in a bin or tray for containing meat or vegetable pieces,the substrate can be substantially the only component that retains thebin/tray shape when separated from the other components. Liner sheetsthat may serve to prevent direct contact between meat or vegetablepieces and the substrate and lidding that may serve to hold such pieceswithin the void of the bin/tray may be unable to retain their shape oncecut or peeled from the substrate, and may contribute to the overallshape and rigidity of the filled bin/tray only to the extent that theyseal the pieces therewithin or overwrap the bin/tray.

In embodiments in which recyclability of the substrate is an importantattribute, the substrate should be a recyclable material and shouldconstitute the majority (on a volumetric or weight basis) of thematerial used to form the article. The quantities of any non-recyclableor difficult-to-recycle liner or lidding material portions of such anarticle are preferably reduced or minimized (relative the quantitiesused in previously-known similar articles), so as to maximize theproportion of materials of the article that can be recycled and toreduce the proportion which must be landfilled, incinerated, or disposedof in another environmentally disfavored manner.

The Liner

The liner sheet must be susceptible of reversible attachment to thesubstrate and attachment (whether or not reversibly) to the lidding. Theliner material should also be selected for physical and chemicalcompatibility of materials that are anticipated to be contained withinthe compartment. The liner can be made from the same material as thesubstrate (e.g., a thinner sheet of the substrate material), butpreferably is not. If the substrate and liner are of the same material,a barrier composition must normally be interposed between them toprevent fusion of the two sheets during thermoforming operations. Ifthey are not of the same material, then the materials, surfacetreatments, and thermoforming conditions should be selected such thatthe materials bind peelably under the thermoforming condition or—if theydo not—a suitable peelable adhesive should be interposed between thesheets.

In an important embodiment of the containers described herein, the linercan be detached from the substrate, preferably without substantialtearing or stretching. The liner should be peelably attached to thesubstrate. Peelable adhesion can be achieved by any of variety ofmethods known in the art. By way of example, a peelable adhesive can beinterposed between the liner and the substrate, or a liner faced with apolymer that peelably adheres to a face of the substrate (e.g., when thetwo faces are pressed together) can be used.

The identity and composition of liner polymer sheets used in thearticles and methods described herein are not critical. A skilledartisan will recognize that substantially any peelable polymericmaterial can be used. Examples of suitable materials includepolyethylenes, polypropylenes, polyethylene terephthalates, nylons,polyvinyl chlorides, copolymers of these, and combinations of these.Plant-based polymers, such as polylactates (also known as “lactic acidpolymers” and PLAs) can also be used.

Because food containers must exhibit numerous properties, use oflaminated polymeric materials is common in food containers, and suchlaminates may be used as the liner sheet in the containers describedherein. Such laminates should include polymer layers that exhibitdesired properties (e.g., tensile strength, vapor/odor resistance,moisture resistance, flexibility, lack of ingredients incompatible withfood, at least in the absence of a barrier layer interposed between suchingredients and the compartment) and sufficient adhesives or tie layersto bind the layers together into a peelable sheet. The outermost polymerlayers have added significance, in that the substrate-side face of theliner sheet must be compatible with reversible attachment of that faceto the substrate (taking into account any materials interposed betweenthe liner and the substrate) and in that the lidding-side face of theliner sheet must be compatible with attachment to the lidding (takinginto account any adhesive or other materials interposed between theliner and the lidding).

Peelable liner sheets preferably have sufficient structural integritythat they do not tear or significantly stretch when subjected to forcesnecessary to peel them from surfaces to which they are adhered. Forexample, when a tray having a peelable liner layer is made as describedherein, the peelable sheet can preferably be peeled from the substrateas a single, integral sheet (i.e., no holes or tears) while notrupturing the compartment defined by the liner and lidding. Peelablesheets that tear, stretch, or puncture are acceptable in embodiments inwhich containment of liquid within the peelable sheet is not required.

The liner sheets are preferably thin and highly flexible. Sheets havinga thickness in excess of 8 mils can be difficult to peel, and so sheetsthicker than that are not preferred. The liner sheets can be made fromsubstantially any polymeric material(s) and by substantially anysheet-forming process. By way of example, suitable polymer sheets can bemade by blowing, molding, casting, or extruding suitable polymermaterials, or by some combination of these processes. When made ofthermoformable materials, the liner sheets are preferably thermoformedsimultaneously with the substrate to which they are adhered. When madeof non-thermoformable materials, the peelable sheets should be capableof maintaining their structural integrity at a thermoforming conditionsat which the substrate sheet to which they are adhered isthermoformable.

Liner sheets can be selected to be rigid (i.e., retain their shape afterpeeling) or substantially non-rigid (e.g., blown polymeric sheets suchas the material used in trash can liners and trash bags).

The peelable nature of an individual liner sheet can derive from surfaceattraction between the liner sheet and the surface underlying it.Alternatively, an adhesive is interposed between the sheet and thesurface and the peelable nature of the sheet derives primarily from theadhesive forces exerted by the adhesive upon the sheet and the surface.An adhesive can be selected (e.g., based on the chemical identity or thesurface treatment of the liner sheet or the surface to which it isadhered) so that, upon peeling of the liner sheet, the adhesivepreferentially remains adhered to the liner sheet, or to the surface(which is less preferable if the surface is the surface of a polymerbody that is to be recycled). For instance, when the function of theliner sheet is to expose the substrate surface free of adhesive andother contaminants, the adhesive can be selected so that it both adheresthe liner sheet and the surface and adheres more strongly (i.e., moretenaciously) to the liner sheet so that, upon peeling, the adhesive isremoved from the substrate along with the liner sheet.

Differences in the tenacity with which an adhesive binds the opposedsurfaces of two polymer sheets can be controlled in a number of ways,including by coating one or more portions of one surface with acomposition that inhibits binding of the adhesive to the surface.Preferably, however, differences in the tenacity of adhesive-binding arecontrolled by selecting or treating the polymer sheets such that theiropposed surfaces exhibit a difference in surface energies. If thedifference between the surface energies of the two surfaces isrelatively large—at least 5 Dynes per centimeter—then the adhesive willbind significantly more tenaciously to one surface than the other. Asthe difference in surface energies of the two surfaces increases beyond5 Dynes per centimeter, the likelihood that all of the adhesive willremain with one sheet when the two sheets are separated increases. Adifference of 5 to 14 Dynes per centimeter between the adhered surfacesof the two sheets is considered appropriate.

It may be possible to separate two surfaces having an adhesiveinterposed between them, even if the surface energies of the surfacesdiffer by less than 5 Dynes per centimeter. In this situation, theadhesive may adhere to each of the two surfaces with roughly equaltenacity, meaning that the adhesive may adhere to both surfaces (atvarious portions) after the two surfaces are separated from one another.In many applications, it is desirable to have most or all of theadhesive to adhere to the surface of only a single one of the polymersheets (usually the one being peeled away from the remaining sheets orsubstrate). For such applications, the two surfaces contacted by theadhesive should preferably have surface energies that differ by at least5 Dynes per centimeter.

The amount of force needed to separate liner sheets from theirunderlying surface is not critical, but is preferably sufficiently smallto prevent tearing and substantial stretching of the peelable sheet uponmanual peeling of the sheet from the surface. The amount of separationforce needed is a function of the materials selected for the linersheets, the underlying substrate surface, and any barrier composition oradhesive interposed between them. Practically speaking, the tenacity ofadhesion between a liner sheet and the underlying surface should beselected so that the sheet can be peeled away from the surface usingnormal human strength, but not so tenacious that the sheet must be tornor punctured by a person peeling the sheet from the surface. A skilledartisan recognizes that the numerous variables (e.g., the angle at whichthe sheet is pulled from the surface, whether fingernails are applied tothe sheet surface, the speed with which the sheet is peeled, thetemperature of the shaped article at the time of peeling) can affect thepeeling characteristics of the sheet, and the materials described hereininclude all materials that are operable under the ambient conditionscorresponding to anticipated uses of the materials and shaped articles.

To the extent that an objective measure of the force needed to peel asheet from an underlying substrate surface is desired, a standardizedtest of peel strength can be used. An example of a suitable test is ASTMD3330/D3330M, which is a standardized test for peel adhesion ofpressure-sensitive tape. A modification of this procedure (e.g.,substituting a sheet of the substrate material in place of the standardsteel sheet in ASTM D3330/D3330M and selecting a peel angle appropriatefor the intended use of the shaped article being tested) can also beused. In each case, the characteristics of the shaped article or stackshould be selected such that the peel strength of the liner sheet fromthe substrate surface is within the limits of ordinary human strength.

Various surface treatments and polymer sheet ingredients can be used toaffect the surface energy. In one embodiment, the substrate and linersheets are made of the same material. Unless treated non-identically,the two faces of a polymer sheet will normally have the same surfaceenergy. Therefore, in containers which include substrate and linersheets of the same material, it is important that the two faces of theidentical polymer sheets be treated differently, so as to yield apolymer sheet having different surface energy values for each of its twofaces. Such sheets are preferably treated such that the surface energiesof their faces differ by 5 Dynes per centimeter or more. Manycompositions and methods for affecting the surface energy of polymersheets are known to skilled artisans in this field, and substantiallyany of those methods may be employed. Such methods include conventionalsurface finishing techniques such as grinding and polishing, quenchingand annealing processes, Corona treatment, and plasma contact techniquessuch as atmospheric, chemical, and flame plasma techniques. Compositionsfor affecting the surface energy of a surface of a polymer sheet arealso well known, and include compounds that can be contacted or reactedwith the surface to modify its chemical or physical properties(affecting its surface energy).

An example of a suitable surface treatment is the process known asCorona treatment or Corona discharge treatment, which involvesapplication to a surface of a high-frequency, high voltage electricaldischarge. Corona treatment raises the surface energy of a polymericsurface. Applied to one face of a polymer sheet having two otherwiseidentical faces, Corona treatment will raise the surface energy of theface, relative to the opposite face of the sheet. The power applied in aCorona treatment can be controlled to limit the treatment substantiallyto one side of a sheet. At very high power, the treatment can raise thesurface energy of both faces of the same sheet which, in the absence ofother surface treatments, will not yield a polymer sheet havingdifferent surface energies on its two faces. If a polymer sheet isCorona treated at or near the time it is formed, the surfaceenergy-raising effects of the treatment can endure for weeks, months, oryears. If the sheet is Corona treated days, weeks, or later after thesheet is made, the surface energy-raising effects of the treatment canbe more transitory (e.g., enduring only for days or weeks). Polymersheets that are Corona treated at or very near the time they are formedcan be used in the containers described herein. Polymer sheets can alsobe “bump-treated” (i.e., be Corona treated regardless of how long it hasbeen since the sheet was formed) shortly before making the stacks andarticles described herein.

The liner sheet can also be attachable to the lidding, preferablywithout the aid of a mechanical device that continuously urges the linerand lidding against one another (i.e., the liner and lidding “stick”without continuously-applied external pressure). Preferably, the linerand lidding adhere to one another or fuse under conditions used tocontact the lidding and the liner. By way of example, if the opposedliner and lidding faces are made from the same polymer, the two sheetscan be caused to fuse if the faces are urged against one another at atemperature sufficient to permit fusion (e.g., the melting temperatureof the common polymer). Alternatively, an adhesive can be interposedbetween the liner and the lidding to form the seal, so long as theadhesive binds both opposed faces.

The seal between the liner and the lidding can be peelable (i.e., thetensile strength of the seal can be less than the tensile strength ofthe weaker of the two polymer sheets), but need not be. When liquidcontainment within (or exclusion from) the compartment is desired, theseal should have sufficient strength (i.e., rigidity and/or resiliency)that the seal will not be breached during anticipated ordinary handlingof the container. The seal between the liner and the lidding can beessentially irreversible, too (i.e., the tensile strength of the sealcan be greater than the tensile strength of the weaker of the twopolymer sheets), in which case opening of the compartment willordinarily be achieved by breaching one or both of the liner andlidding, rather than by separating them along the seal.

The material used as the liner should be selected to exhibit sufficientbarrier properties to exclude from the interior of the compartment anymaterial(s) that are anticipated to be present at the substrate face ofthe liner under conditions of ordinary use of the container, taking intoaccount both materials present in the substrate and materials present inany adhesive, barrier compositions, additional polymer sheets, or othercomponents interposed between the liner and the substrate. Selection ofmaterials based on their barrier properties is routine in the art, givenknowledge of the material(s) for which migration is to be avoided.

In a preferred embodiment, the liner material is peelably adhered to thesubstrate and is closely opposed against a surface of the substrate,such that it can be difficult for an ordinary observer to tell that theliner is present, except perhaps at a selected area where a tab orfolded portion of the liner is present to facilitate peeling thereof. Inanother embodiment, the materials or characteristics (e.g., color) ofthe substrate and the liner are selected to clearly differentiatewhether or not the liner and the substrate are adhered. By way ofexample, a white liner can be applied against the face of a blacksubstrate, such that the presence of the liner is obvious. The liner,the substrate, or both can also carry an indicia (e.g., a stripe, anarrow, or the text “PEEL HERE”) that highlight a portion of thecontainer at which peeling of the liner from the substrate can beinitiated.

The liner should also be selected to have sufficient barrier propertiesto maintain desired conditions within the compartment, taking intoaccount barrier properties of the substrate at positions at which theliner and substrate are laminated. Food containers are commonly intendedto maintain a desired atmosphere (i.e., gas content and/or humidity),presence or absence of compounds within the compartment, or otherphysical or chemical characteristics in the compartment in which afoodstuff is contained. By way of example, foodstuffs that arerelatively susceptible to discoloration or degradation in the presenceof atmospheric levels of oxygen are sometimes packaged in an atmospherefrom which oxygen is substantially depleted, such as a nitrogen, argon,carbon dioxide, or carbon monoxide atmosphere. Such packaging techniquesare commonly referred to as modified atmosphere packaging or MAPtechniques.

For containers intended for use in combination with desired compartmentconditions, a liner material capable of maintaining those conditionsunder the conditions of anticipated use of the container should beselected. Such selection is within the ken of a skilled artisan in thisfield.

By way of example, meat and poultry products can be packaged in acontainer in which the substrate is made from a PET material (e.g.,amorphous PET or PETG) and each of the liner and the lidding are alaminate polymer material. In this example, the liner can have asubstrate-side face composed of ULDPE or LLDPE, a nylon lamina to confertensile strength to the liner, an EVOH or PVOH lamina to inhibitmoisture and vapor passage through the liner, and a lidding-side facecomposed of a material identical to the liner-side face of the lidding(i.e., to facilitate heat fusion of the liner and lidding uponapplication of heat to the opposed faces). The lidding in this example,can have the same layers as the liner. In one embodiment, the liner andthe lidding are identical (e.g., viewed in cross section, the two sheetshave the identical composition, only in an inverted configuration, suchthat ‘top’ of one sheet contacts the ‘top’ of the other), such as anembodiment in which a portion of the liner is laminated against a convexsurface of the substrate and a second portion of the liner forms a flapthat can be folded across the opening of the convex surface and sealedagainst itself (i.e., the liner and the lidding are part of the samesheet of polymer or laminate).

In embodiments in which a rapidly-quenched polymer sheet is used topromote adhesion, it can be preferable that a face of the sheet that wasdirectly quenched (e.g., the face against which water was applied in awater-quenched blow extrusion process, the face opposed against achilled metal surface in a casting process, or a face contacted againsta chilled extrusion die) be applied against the sheet to which it is tobe adhered. Thus, for example, in articles in which a rapidly-quenched,relatively thin liner sheet having an EVOH layer sandwiched between twoLLDPE layers is adhered against an ordinary (i.e., notrapidly-quenched), relatively thick PET substrate sheet, a LLDPE face ofthe liner sheet against which a quenching agent was applied in order toeffect rapid quenching is the face that is preferably applied againstthe PET substrate. In this example, the liner sheet can be laminatedagainst the PET substrate sheet using a cold-nip roller, and theresulting laminate can be thermoformed and cut to yield the shapedarticle, such as a tray from which the liner can be peeled. If, in thisexample, the PET sheet was also rapidly quenched, the directly quenchedface of the PET could be applied against either face of the liner sheet,just as the directly quenched face of the liner sheet could be appliedagainst either face of the substrate sheet. Enhanced adhesion can beexhibited by laminates in which both opposed faces of adjacent sheetsare the directly quenched face of a rapidly-quenched polymer sheet. Byselection and arrangement of the directly quenched face(s) of laminatedsheets, a skilled artisan in this field is able to obtain and selectamong a variety of useful configurations.

Because containers can be subjected to a wide variety of ambientconditions, containers that will be so subjected should be constructedusing a liner material that has about the same coefficient of thermalexpansion (“shrink rate”) as the substrate.

The Lidding

The identity of the materials used as the lidding is not critical, otherthat that the lidding should be attachable to the liner and shouldexhibit any properties (e.g., tensile strength, barrier properties,ability to carry printing or adhesive labels, and surface appearance)required for the desired application. The lidding material can be thesame material as the liner, or it can be different.

In one embodiment, the container is supplied in the form of a kit thatincludes a shaped substrate (e.g., a tray or bowl) that has a linerpeelably laminated against a face thereof and a separate liddingmaterial, supplied either as a roll or as a piece of lidding having asize and shape corresponding to the portion of the shaped substrate towhich the lidding will be applied and attached to the liner.

In another embodiment, the container is supplied in the form of a shapedsubstrate (e.g., a bowl or tray) having a liner peelably laminatedagainst a face thereof, with the lidding present as an extension of theliner and shaped and positioned such that the extension can be foldedacross the portion of the substrate bearing the liner and attached tothe liner (e.g., “a bowl with a flap,” the flap having a size and shapesufficient to cover the shape of the bowl with sufficient overlap alongthe periphery thereof to permit sealing between the flap and the portionof the liner borne by the periphery of the bowl, and the flap beingpositioned and dimensioned such that it can be folded across the orificeof the bowl and contact the liner about its periphery to facilitate suchsealing about the entire periphery).

In yet another embodiment, the container is supplied in the form of anon-shaped (i.e., substantially flat or planar) piece of substratematerial having a piece of liner material opposed against it (with orwithout additional polymer layers, adhesives, barrier compositions, orother materials interposed between the pieces). The substrate and linercan be simultaneously thermoformed and the lidding thereafter attachedto the liner. In still another embodiment, the liner and the lidding areattached to one another (forming the compartment and optionallyenclosing an article) prior to reversibly attaching the liner and thesubstrate.

Adhering Polymer Sheets

As disclosed herein, various layers (sheets) of polymeric materials areintended to be combined to form laminated containers and other articles,but the layers/sheets are intended to remain separable from one another(e.g., peelable using ordinary human strength) in many embodiments. Theadhesives described herein can be used to assemble such laminatedstructures. However, in some applications (e.g., food containers), it ispreferable that the laminated structures be made in a manner that doesnot involve interposing an adhesive between laminae, but nonethelessyields laminated articles in which the laminae remain relatively fixedlyassociated with one another until a lamina is peeled from the article bya user. Disclosed herein are polymer sheets which peelably adhere to thesurface of other polymers without the use of an interposed adhesive, aswell as methods of making and using such sheets.

It is well known that dissimilar polymer sheets (e.g., barefoot PE andPET sheets) will generally not adhere to one another absent staticcharge differences, the presence of an interposed wetting agent,sealant, or adhesive, co-extrusion of the polymer layers, inclusion ofadherence-promoting additives in one or both sheets, or heating one orboth polymer sheets above its melting point while urging it against theother. Although these methods can be used to adhere polymer sheets,their utility is limited for making some of the laminated articlesdescribed herein.

By way of example, owing to government regulations, good manufacturingpractices, and the added cost of interposing an agent (e.g., anadhesive) between adjacent polymer sheets, many chemicals are not usedin food packaging materials, and food containers preferably do notinclude unnecessary components. For that reason, it is preferable tomake containers that lack adhesives, wetting agents, or other chemicalagents interposed between polymer layers. Some of the articles describedherein can be used for containing food, and contact between the food andinterlaminar adhesives or other agents (whether direct contact orindirect contact, such as by migration of such agents across or aroundpolymer layers) can raise contamination and regulatory concerns. Atleast in some embodiments, the food containers (and other containers)described herein preferably do not include adhesives or other materialsinterposed between peelable polymer layers, and instead incorporateadherable polymer sheets as described in this section.

Methods of rendering polymer sheets peelably adhered to one another canalso impose manufacturing limitations that render such methodsimpractical for use on a large scale. By way of example, some PE filmscan be peelably adhered to PET substrates if the PE is heated above itsmelting point and compressed against the PET. Thus, for example, a 2 milPE sheet can be peelably adhered to a 20 mil PET substrate by stackingthe two sheets and passing them through a hot nip roller that inducesmelting of the PE. However, such processes can be limited by the rate atwhich the hot nip can transfer heat to the PE film, which leads torelatively slow processing speeds and impracticality in commercial-scalemanufacturing. Similarly, it can be difficult to adequately and reliablydeliver adhesives and wetting agents between two polymer sheets at highprocessing speeds. Articles made using adherable polymer sheets cangenerally be manufactured at greater line speeds because these processlimitations are not present.

Interposition of adhesives, wetting agents, or other materials betweenpolymer sheets can also reduce the recyclability of the “webbing” (i.e.,laminated polymer material trimmed or excluded from manufacturedarticles during the manufacturing process) that is produced as aby-product of the thermoforming manufacturing process. Because thelaminated polymer sheets of the webbing can be separated from oneanother without having an adhesive or other agent adhered to eithersheet, the resulting separated sheets can be more easily recycled orre-used than sheets from similar processes that employ such agents.

It has been discovered that laminated articles described herein can bemade using polymer sheets that can be peelably adhered to one anotherwithout the use of interposed adhesives or wetting agents and withoutapplication of heat prior to thermoforming. Polymer sheets that peelablyadhere to other polymers include especially those in which the face ofthe sheet to be adhered to the other polymer has been rapidly quenched,such as by liquid quenching in a blow-molding process or by liquid (orliquid-cooled metal surface) quenching in a sheet-casting process. Suchsheets can be peelably adhered by opposing the rapidly-quenched faceagainst the other polymer and urging the sheet toward the other polymer,such as by using a cold nip roller process. The rapidly-quenched facecan be a face of a thin liner sheet urged against a face of a relativelythick substrate sheet. Alternatively, a face of a relatively thicksubstrate sheet can be rapidly-quenched and urged against a face of arelatively thin liner sheet. In either configuration, urging therapidly-quenched face against the other will cause the two faces toadhere, especially if the two faces are urged together coherently over alarge area, such as by compressing the two sheets against one anotherbetween a roller and another surface such as a second roller. In fact,both of the opposed faces can be rapidly-quenched.

The properties of rapidly-quenched polymer sheet faces that result inpeelable adhesion are believed to include its tackiness, deformability,and cohesiveness. In this context, “tackiness” relates to exhibition ofthe tactile sensation of stickiness, at least to a small degree, such asa feeling of releasable adhesion to a human finger pad when the fingeris pressed lightly against the surface in a direction perpendicularthereto and withdrawn in the same direction. “Tackiness” also relates toexhibition of friction, as measurable by the coefficient of staticfriction measurable when the rapidly-quenched polymer face is appliedagainst a substrate face. A relatively tackier material will exhibit agreater coefficient of static friction when at rest against a substratesurface than a less tacky material at rest against the same surface.“Deformability” relates to the ability of the rapidly-quenched polymerface to be displaced from its original conformation and more nearlymirror the conformation of a polymer surface against which it is urged.“Cohesiveness” relates to the ability of the rapidly-quenched polymerface to remain a substantially unitary polymeric mass (i.e., withoutsplitting or fracturing) when urged against a polymer surface.

Although the materials described in this section are referred to as“rapidly-quenched” polymer sheets, the utility of these materials doesnot necessarily depend on the duration of the quenching period. Instead,it is the combination of properties (i.e., tackiness, deformability, andcohesiveness) that are exhibited by rapidly-quenched polymer sheet facesthat lend utility to the materials. It is recognized that skilledartisans in this field are able to mimic the surface and bulk propertiesof polymer sheets that are attainable by rapid quenching through use ofmethods and reaction conditions that do not depend solely on thetemporal duration of polymer annealing. By way of example, annealing ofpolymer strands and their distribution among amorphous and crystallineregions can be affected by humidity, temperature, the presence ofsolvents, the presence of nucleating agents (or anti-nucleating agents),and other factors known in the art. Without being bound by anyparticular theory of operation, it is believed that reducing the degreeand extent of crystallinity at the surface of a polymer sheet is animportant factor for enhancing the tackiness of a polymer surface, andmethods and reaction conditions that will tend to reduce the degreeand/or extent of crystallization are preferred. Still without beingbound by any particular theory of operation, it is believed thatrelatively low density is another favorable characteristic induced byrapid quenching at polymer surfaces, although it is unclear whether therelatively low density is causative of tackiness, coincidental withtackiness, or both. Relatively low density is, for most polymers,coincidental with a less-ordered (e.g., less crystalline) polymerstructure. Furthermore, phase conversions among polymer phases havingdifferent densities can contribute to adhesion in polymers capable ofundergoing such conversions (e.g., upon compression between rollersduring lamination).

Whether adhesed with or without an interposed adhesive, the degree ofadhesion that is usefully attained between a liner sheet and an opposedsubstrate sheet is preferably a sufficient degree of adhesion that theliner and substrate can be laminated and thermoformed into a shapedarticle without substantial delamination of the liner from thesubstrate. More preferably, the degree of adhesion is sufficient thatthe article can be not only formed without substantial delamination, butalso employed for its intended end use without substantial unintendeddelamination. Depending on the application and use of the article, agreater or lesser degree of adhesion can be desirable between adjacentliner sheets, particularly for applications and articles intended tohave separately-peelable liner layers.

By way of example, for the food container described herein having athick, rigid substrate with a liner peelably adhered thereto, the linerhaving a lidstock material bound about its periphery to form a peelableleak-proof ‘pocket,’ the liner preferably adheres to the substrate to asufficient degree that the liner and substrate can be laminated andthermoformed into the shape of a tray without the liner delaminating toa substantial degree from the substrate (other than at anintentionally-formed tab, for example, the tab included to facilitatepeeling of the liner from the substrate). More preferably, a foodstuffcan be placed upon the tray and a lidstock heat-sealed to the linerabout the foodstuff (e.g., under vacuum to remove gases from between theliner and the lidstock) to form a leak-proof, foodstuff-containingpocket adhered to the tray, and the degree of adherence between theliner and the substrate is sufficient that these operations can beperformed without the liner substantially delaminating from thesubstrate. Still more preferably, the degree of adherence is such that,even when the packaged foodstuff is subjected to the handling andstorage conditions normally incident to wholesale and retail sale of thefoodstuff, substantially no delamination of the liner from the substrateoccurs until such delamination is intentionally initiated by anindividual desiring to consume the foodstuff.

A skilled artisan in this field understands that the coefficient offriction and other characteristics of two adhered polymer sheets aretypically assessed empirically, and that the magnitude and combinationof characteristics that are desirable for a selected article orapplication tend to be functionally, rather than numerically, defined.Thus, a skilled artisan attempting to make and use the articlesdescribed herein will often select materials that are empiricallydetermined, through reasonable trial-and-error, to exhibitcharacteristics sufficient to achieve the desired end, taking intoaccount what is taught in this disclosure.

While not being bound by any particular theory of operation, it isbelieved that relatively rapid quenching of a polymer tends to preservethe amorphous configuration of polymer strands relative to one anotherand reduce crystallization of polymer strands, while slower quenchingfacilitates formation of crystalline and other ordered polymerconfigurations. It is believed that a relatively disordered polymerstrand conformation promotes (more so than do ordered conformations) theability of polymer strands to bind with surfaces they contact, becausechemical moieties on the strands that exhibit binding capacity are notbound to other strands of the same polymer and therefore remainavailable to bind with moieties at the surface. It is also believed thata relatively disordered polymer strand conformation promotes (more sothan do ordered conformations) the ability of polymer strands to bedisplaced upon being urged against such a surface. Thus, it is believedthat rapidly quenched polymer materials can conform more closely againstan opposed surface and present a greater number/concentration ofsurface-binding moieties than can more slowly quenched materials, eventhose composed of the same polymer. By contrast, strands inslowly-quenched polymers can rearrange themselves to assume more stableconformational and energetic inter-strand configurations, therebyreducing their ‘adhesive reactability’ with a surface against which suchslowly-quenched polymers are urged.

The degree of crystallinity is known to affect the barrier properties ofpolymer sheets in relatively predictable ways. By way of example, theoxygen permeability of nylon and EVOH films tends to decrease as thedegree of crystallinity increases. Thus, selection of polymers for linerand substrate sheets (and layers within sheets) should take thosecharacteristics into account. By way of example, the EVOH layer of aliner sheet formed by sandwiching an EVOH layer between two LLDPE layerscan have higher oxygen permeability if the sheet is formed byliquid-quenched blow extrusion than if a sheet having layers withidentical dimensions and compositions is formed by ordinary (air) blowextrusion processes. In such an instance, the thickness of the EVOHlayer of the liquid-quenched blow extruded liner sheet may need to beincreased if the sheet is to exhibit the same oxygen barrier propertiesas the (air) blown sheet. Such modifications of known polymer sheetdesigns are within the ken of the skilled artisan in this field, even ifempirical trials may be necessary.

Tackiness and deformability of the rapidly-quenched polymer are believedto be related, in that as deformability of the polymer increases, lesstackiness is required in order to peelably adhere it to a polymersurface. Similarly, it is believed that as tackiness of the polymerincreases, less deformability is required in order to peelably adhere itto a polymer surface. A skilled artisan in this field understands that apolymer compositions, properties, and production methods are oftenadjusted through reasonable empirical trials, and such trials are wellwithin the ken of such an artisan.

The adhesive force between the quenched polymer face and the polymersurface to which it is adhered should be sufficient to maintain theadherence during manufacture of the articles described herein and theirordinary (pre-peeling) use. The tenacity with which the quenched polymerface and the polymer surface are adhered should not be so great that thetwo polymers cannot be separated by a user of ordinary human strength,and should also not be so great that either polymer will tear prior topeeling from the other. By way of example, in a retail food container inwhich a rapidly-quenched polymer sheet is used as a liner for asubstrate, the liner should adhere to the substrate sufficientlytenaciously that it remains adhered thereto as the container is made,shipped to a food processor for filling, and used to contain a foodthrough processing, shipment, and wholesale and retail sale.

A drawback of insufficient adherence between a liner sheet and asubstrate sheet is that air pockets can be included between the sheetsduring lamination if the sheets are not uniformly pressed against oneanother. Formation of such air pockets can also be induced if thelaminated sheets are too sharply ‘pinched’—i.e., if the laminated sheetsare caused to deflect from a planar conformation and the radius ofcurvature of the deflection is too small. When a laminated sheet havingan air pocket between its lamina is thermoformed, the heat of thethermoforming can cause the air in the pocket to expand and preventadhesion between portions of the sheet that were intended to be adhered.The materials and processes used to make the shaped laminated articlesdescribed herein should therefore be selected to reduce occurrence ofair pockets. Two significant ways in which air pocket occurrence can bereduced are by laminating sheets flush against one another (i.e., withflat faces opposed against one another, substantially without wrinkles,such as by passing through hot or cold rollers) and by reducing thecurvature angle of any deflections to which the laminated sheets aresubjected. By way of guidance, many thermoforming andplastic-sheet-laminating processes can be performed without causing thesheets to bed around any corner having a radius of curvature less thantwo inches; selection of materials which, when adhered flush against oneanother and bent about a corner having a radius of curvature of twoinches or more, remain laminated and do not admit air pockets betweenthe sheets should be suitable for making the articles described herein.

Such containers can be sold in the form of a kit, the kit including asubstrate having a polymeric liner sheet adhered thereto by way of arapidly-quenched face and a lidding material adapted for binding (byadhesion, adherence, or fusion) with the liner sheet. Using such a kit,food processors, retailers, or others can place an article (e.g., afoodstuff) on or in the container at a surface at which the articlecontacts the liner and seal the article within a compartment by bindingthe lidstock to the liner about the article.

The material(s) from which the adherable polymer sheets described hereinare made is not critical, other than that it should be capable ofexhibiting the properties described herein. By way of example, PEs andother polyolefins are believed to be suitable materials which can berapidly quenched and, when so quenched during their manufacture, willexhibit the properties described herein. Suitable adherable polymersheets have been made by rapid quenching of PE and ULDPE polymers, forexample, and those rapidly-quenched polymer faces exhibited peelableadherence to smooth PET substrates when compressibly urged togetherusing a cold nip roller followed by thermoforming.

Multilayer films having a rapidly-quenched surface can be used as theadherable polymer sheets, so long as the rapidly-quenched polymer ispresent on at least one surface of the sheets. Sheets havingrapidly-quenched polymer on both faces are suitable, and can bemanufactured, for example by adhering, back-to-back, two sheets having arapidly-quenched polymer face on their front faces. Such dual-facedsheets can be used to peelably adhere two polymer substrates to oneanother by compressing a stack having the two substrates with thedual-faced sheet interposed therebetween.

The properties of the surface to which adherable polymer sheets areadhered are not critical. Such surfaces should, however, be relativelysmooth so as to facilitate close opposition of the sheets thereto andbinding between the rapidly-quenched polymer layer and the substrate.Polymeric substrates (e.g., PETs, PETGs, polystyrenes, and the like) areconsidered suitable and other polymers undoubtedly are as well.

The method of manufacturing the adherable polymer sheets describedherein is not critical, and indeed appears to be far less important thanthat the face of the polymer sheet that is adherable be rapidly quenchedfrom a melted state during its manufacture. A preferred method ofmanufacture is by liquid-quenched blow extrusion processes. Equipmentfor performing liquid-quenched blown film extrusion is available from atleast two manufacturers, Windmoeller & Hoelscher Corporation (Lincoln,R.I.; especially their AQUAREX brand water-cooled blown film extrusionapparatus) and Brampton Engineering (Brampton, Ontario, Canada;especially their AQUAFROST brand water-cooled blown film extrusionapparatus). Various film casting systems can also be used, so long as atleast one face of the film is made of a polymer capable of exhibitingthe properties described herein upon rapid quenching and that face israpidly quenched.

Rather than rapidly quenching an entire polymer sheet, only one or moreportions of such a sheet can be rapidly quenched. By way of example, amolten polymer extrudate can be layered onto an existing film and thenrapidly quenched (e.g., by flooding the molten face with liquid, byimmersing in liquid the film carrying the molten face, or by compressingthe molten face against a liquid-cooled metal surface, such as a metalroller having chilled water circulating therein or a liquid-cooled dieconnected with an extruder). Further by way of example, a polymer sheetcan be formed in a conventional way, with no face thereof being rapidlyquenched. A face of the sheet can thereafter be melted (whether or notother portions of the sheet are melted) and the molten face rapidlyquenched.

In one embodiment, stacks of polymer sheets suitable for thermoforminginto shaped articles having a peelable surface (e.g., food containers)are made by laminating at least two polymer sheets, with at least one ofthe opposed faces of two adjacent sheets having the rapidly-quenchedsurface with the properties described herein. Upon lamination (e.g., bypassage of the stacked sheets between a cold nip roller or othercompressing apparatus), the sheets become peelably adhered to oneanother. More than two sheets can be peelably laminated in this manner,provided that at least one surface between each pair of adjacent sheetshas the rapidly-quenched surface with the properties described herein.Of course, multi-sheet laminates can also be made in which some adjacentsheets are peelable on account of the presence of the rapidly-quenchedsurface with the properties described herein and other adjacent sheetsare peelable on account of the presence of a peelable adhesiveinterposed between them.

In another embodiment multiple identical sheets are layered atop asubstrate and are individually peelable from the construct, on accountof there being a rapidly-quenched surface with the properties describedherein at at least one face of each pair of adjacent sheets. Thus, forexistence, a recycled PET substrate can be coated with multiple stackedsheets of a bi-layer film, each sheet of the bi-layer film having arapidly-quenched ULDPE layer tied to a virgin PET layer. Therapidly-quenched ULDPE layer of the sheet adjacent the substratepeelably adheres to the substrate and displays the virgin PET layer onits opposite face. Stacked thereon is a second sheet, such that itsULDPE layer peelably adheres to the virgin PET layer of the first sheet,the second sheet having its virgin PET layer situated distally from thesubstrate. Additional layers can be stacked thereon, and the stack canbe thermoformed, the thickness of the stack being limited substantiallyonly by the operating characteristics of the thermoformer and thethermformability of the polymers in the stack. Similarly, the firstpolymer sheet (adjacent the substrate) can have rapidly-quenched ULDPEtied to both faces of a PET sheet, such that it peelably adheres to thesubstrate at one face and presents at its other face a rapidly-quenchedULDPE layer that can be peelably adhered to the virgin PET layer of thePET-ULDPE bilayer sheet. Additional bilayer sheets can be layeredthereon, each with its PET face proximally facing toward the substrate.

Making the Container

The articles described herein can be made using known thermoformingapparatus and conditions. Of course, the apparatus and conditions shouldbe selected based on the identity and the characteristics of thematerials to be processed. Selection of appropriate thermoformingconditions, based on the identity(ies) of the materials to be processedis within the ken of a skilled artisan in this field.

The container is formed by reversibly attaching the liner to thesubstrate and by attaching the lidding to the liner to form thecompartment for containing material.

The substrate can be formed into a desired shape before or afterdetachably attaching the liner thereto. However, at least forthermoformed containers, it can be convenient to simultaneously (ornearly simultaneously) attaching the liner to the substrate and formingone or both of the liner and substrate. Preferably, the substrate has athickness substantially greater than the liner (e.g., a 10, 20, or 50mil substrate can be bound with a 1, 2, or 5 mil liner). Preferably,both the liner and the substrate are thermoformable, and preferably at acommon thermoforming condition.

In one embodiment, the substrate, the liner, and the lidding aresimultaneously subjected to the thermoforming condition, and reversibleattachment of the liner and substrate and attachment of the liner andlidding occur substantially simultaneously in the thermoformingoperation. Containing an article within the compartment of a containermade in this way requires either that the compartment remain open afterthermoforming operation or that the article be interposed between theliner and lidding sheets during thermoforming, so that the article iscontained within the compartment following thermoforming.

One or more tabs can be interposed between the substrate and the liner,between the liner and the lidding, or both. If a tab extends beyond anedge of two sheets, the tab can be used to facilitate separation of thefirst sheets after thermoforming or sealing. The tab can be adhered toeither sheet or to neither.

In one embodiment, the tab is relatively fixedly adhered to the lowersurface of a liner sheet that overlies the substrate. The tab is eitherpeelably adhered to or not adhered to the underlying substrate, suchthat the overlying liner sheet can be peeled from the underlyingsubstrate by grasping the tab and pulling the overlying sheet by way ofthe tab. The tab can, for example, be formed by folding a piece (e.g., acorner) of the liner over itself.

In a second embodiment, the tab is relatively fixedly adhered to theshaped surface of the substrate and either peelably adhered to or notadhered to the overlying liner sheet, such that the overlying linersheet can be peeled from the surface by scratching (e.g., with afingernail or an edged instrument, such as the tine of a fork) the edgeof the overlying liner sheet that overlies the tab to begin partialpeeling of the overlying liner sheet at the location of the tab, andthen grasping the partially peeled portion of the overlying liner sheetand manually peeling the remainder of the overlying liner sheet awayfrom the surface by pulling on the partially peeled portion.

Although a loose stack of polymeric sheets can be thermoformed using thematerials and methods described herein, it can be convenient to bind thesubstrate and liner sheets to one another prior to thermoforming (e.g.,to facilitate combination, storage, shipping, handling, manufacture, andalignment of the sheets). The means used to bind the sheets to oneanother is not critical, but preferably does not affect the propertiesof the sheets in the region(s) of the sheets that are to bethermoformed. By way of example, the sheets can be bound together usinga glue applied to a common edge of the first and second sheets, byfusion of a common edge of the sheets, by stapling the sheets together,by adhering the sheets together using an adhesive applied between thesheets at an inter-sheet area distinct from the shaped section of thesheets, or by other means, such as providing a continuous (i.e., muchlonger than it is wide) roll of substrate sheet having the liner sheetadhered thereto or opposed against it.

Readily Peel Able Lidstock-Liner-Substrate Configurations

Benefits (e.g.. recyclability) of food trays and other containers havingpeelable liners are described elsewhere herein, as are those of traysand other containers which further include lidstock material attached tothe uppermost liner to form a sealed compartment. It can be beneficialto make containers from which the liner and the lidstock can be removedwithout necessarily breaching the compartment. The ease from which thecompartment can be removed intact from the container substrate canaffect the desirability of the container to the user who will performsuch removal. Such containers can be displayed at the point of sale ofarticles contained therein, in which instance the appearance of thecontainer is also important. Described in this section is aconfiguration of the substrate, line(s), and lidstock that can exhibitthese properties.

In this configuration, the lidstock and the liner are adhered to oneanother more tenaciously than the liner is adhered to the surfaceunderlying the liner at at least one portion of the container,preferably along the perimeter of the container. Moreover, that zone ofrelatively tenacious binding should preferably occur along one edge ofat least the liner sheet, so that the compartment formed between theliner and the lidstock can be readily peeled intact from the surfaceunderlining the liner by grasping and peeling the lidstock. Because thelidstock is relatively tenaciously adhered to the liner at the edge ofthe liner, lifting the lidstock towards the liner will commence peelingof the liner from the substrate as the lidstock is lifted away from thesubstrate at the edge of the liner. This configuration facilitatesmanufacture of a container from the thermoformable stack describedherein by applying lidstock thereto, such as in conventional ways.

In one configuration, a relatively thick substrate (e.g., 20-40 milthick PET) has a single relatively thin liner (e.g., 1-6 mil thick)adhered thereto. In this embodiment, the thin liner is a homopolymersheet, such as a polyethylene sheet, that is peelably adhered to thesubstrate across substantially an entire face of the substrate. Thesubstrate and adhered liner have a shape (e.g., formed by thermoformingthe stacked sheets) that includes a concave portion having a rimsurrounding it, the rim preferably being substantially planar such thata flat sheet that contacts the rim about the perimeter of the concavityseals the concavity. A lidstock material (e.g., a 1-10 mil thickhomopolymer or laminated polymer sheet) contacts the liner about the rimof the concavity, and is preferably taut, such that the lidstockmaterial has a substantially planar shape within the perimeter of theconcavity. The lidstock is adhered or fused to the liner at at least oneportion of the rim, and is preferably adhered or fused to it around theentire perimeter of the concavity. If the liner and the face of thelidstock that contacts it are made of substantially the same material(the necessary degree of identity being understood by those skilled inthe art), then the liner and lidstock can be fused by heating each abovethe melting temperature of the material, contacting the liner andlidstock (preferably urging them against one another, such as by forminga high-impact seal or a low-impact seal, as these terms are used in theplastic packaging arts), and then cooling the materials below themelting temperature. The liner is adhered or fused to the lidstock at atleast one edge of the liner/substrate stack. The adherence or fusion issufficiently resilient that the liner peels from the substrate when thelidstock is pulled in a direction away from the substrate. The resultingpackage is useful for enclosing articles (e.g., food articles orliquid-sensitive components) within the compartment formed between thelidstock and the liner while the liner is engaged with the substrate,and for peeling the compartment from the substrate (e.g., by peeling thelidstock therefrom at a position at which it is adhered or fused to theedge of the liner/substrate stack) without necessarily breaching thecompartment. Optionally, the container can include a zipper-typereclosable opening disposed either in the lidstock or between thelidstock and the liner, for facilitating access to and reclosing of thecompartment between the lidstock and liner.

In alternative embodiments, the container includes more than one liner,such as an embodiment in which a compartment that includes a fluidreservoir formed between a perforated and a non-perforated liner, withat least one of the liners adhered to or fused with the lidstock. By wayof example, the container can have a substrate formed to include aconcavity and having a non-perforated liner peelably adhered to thesubstrate at least at the portion thereof that defines the concavity, aperforated liner fused with (optionally adhered to) the non-perforatedliner about the rim of the concavity, and a lidstock adhered to or fusedwith the perforated liner about the rim of the concavity, including upto an edge of the perforated liner. When the lidstock is peeled awayfrom the substrate, at least the perforated liner (and optionally thenon-perforated liner, such as if it is fused with the perforated liner)is pulled away from the concavity, taking with it any objects within thecompartment between the lidstock and the perforated liner that cannotfit through the perforations. If the non-perforated liner is notsimultaneously peeled from the substrate, then materials (e.g., liquid)capable of passing through the perforations can be separated from othermaterials in the compartment and can remain associated with thesubstrate (and can be subsequently dissociated from the subject bydumping or pouring, or by peeling the non-perforated liner from thesubstrate). If the non-perforated liner is fused with the perforatedliner about the rim, for example, then peeling the lidstock away fromthe container without separating the lidstock and liners from oneanother will peel away a compartment that can contain both materialslarger than the perforations and materials smaller than the perforation.Thus, for example, such a container can be used to contain a cut of meatwithin a concavity of the container, liquid exuded by the meat can passinto the fluid reservoir between the perforated and non-perforatedliners, the meat can be removed in a sealed compartment from thesubstrate, and any exuded liquid can be either removed at the same time(by peeling the non-perforated liner from the substrate simultaneouslywith peeling the lidstock) or after the compartment has been removed (bypeeling the lidstock and associated compartment first, and thereafterpeeling the non-perforated liner from the substrate).

In various embodiments, one or more of the liners and the lidstock canbe multi-laminate polymer sheets, such as sheets having various polymerlaminae that confer barrier properties, tensile strength, adherability,ability to fuse with opposed polymer faces, ability to link adjacentlaminae, or other properties. The liners and lidstock can also behomopolymer sheets.

The substrate can have multiple concavities, and each concavity thereincan be covered with the same liner sheet(s) or different liners. Some orall of the concavities can have a single piece of lidstock appliedthereto. Similarly, multiple pieces of lidstock (composed of the samematerial or different materials) can be fixed around or across a singleconcavity (e.g., two pieces of closely-spaced lidstock having paralleledges can be fixed across a concavity to yield a compartment that isclosed other than at a slit defined by the edges of the lidstock pieces.For ease of manufacture, filling, and assembly, it is preferred tomanufacture containers in two pieces: a first piece including thesubstrate and all liners peelably bound thereto (with the shape,including any concavities, preferably formed by thermoforming asubstrate-liner(s) stack) and a second piece including the lidstock;thereafter to fill the containers with desired items (e.g., electroniccomponent parts or poultry parts within concavities); and thereafter toseal the lidstock to the shaped and filled liner-substrate piece. Thefirst piece can include multiple separable containers, each having aconcavity and being separable by cutting or tearing the first pieceafter the lidstock has been sealed thereto.

Containers of the type described in this section can be particularlybeneficial if they are formed and shaped in a manner that facilitatespeeling of at least one liner from the substrate upon peeling of thelidstock from the substrate. This can be achieved by adhesing or fusingthe liner and the lidstock at an edge of the liner, so that peeling thelidstock past the adhesed/fused edge initiates peeling of the liner fromthe surface underlying it (i.e., from the substrate or from anotherliner interposed between the substrate and the liner adhesed/fused tothe lidstock). Such adhesion/fusion can be accomplished by adhesing orfusing the liner and lidstock prior to adhering the liner. However, suchmanufacturing methods can be difficult to perform and can interfere withpackaging of items between the liner and the lidstock. More typically,the substrate-adhered liner will be manufactured separately from thelidstock and the lidstock and liner are adhesed or fused after packagingan item within the compartment formed between the liner and thelidstock.

The edge of a liner can be adhesed or fused with lidstock by bringingthe edge of the liner in contact with the lidstock during theadhesion/fusion process. For ease of manufacture, for the purpose ofstrengthening edges, and for aesthetic reasons, thermoformed containersoften have curved or bent edges. Binding lidstock to the edge of thecontainer is typically not of particular concern in prior artcontainers. Instead, lidstock is usually trimmed near the edge of thecontainer after being applied thereto, and the edge of the lidstock issometimes heated so that it either curls around the edge of container orshrinks to more closely fit against that edge. In the configurationdescribed in this section, it is important that the edge of a lineradhered to the substrate bind relatively tenaciously to the lidstock(relative to the tenacity with which the liner binds to the substrate),so that the liner can be peeled from the substrate upon peeling of thelidstock therefrom. In order to facilitate binding of the liner edge tothe lidstock, the liner edge should be brought into close opposition tothe lidstock upon binding (by adhesion, adherence, fusion, or otherwise)of the lidstock and the liner. Such close opposition can be achieved insubstantially any manner known in the art.

One way in which the edge of a liner and lidstock material can bebrought into close opposition during binding therebetween is by urgingthe lidstock and liner together in a conformation in which the edge ofthe liner is held against the lidstock during application of ambientconditions (e.g., temperature, irradiation, pressure, or provision of anadhesive) that cause binding of the lidstock and portions of the linerwhich contact it. By way of example, a liner having a lidstock-bindingface composed of the same material as the liner-binding face of alidstock material can be caused to bind with the lidstock material bycontacting the two faces at a temperature at or greater than the meltingtemperature of the common material.

When the location is known at which peeling force applied to a lidstockmaterial will be transmitted to a liner bound to the lidstock, closeopposition of the lidstock and liner can be preferentially maintained atthat location during liner-lidstock binding. Similarly, the location atwhich such close opposition is maintained during liner-lidstock bindingcan be indicated on the finished container, so that the location can beselected by a user of the container as an appropriate location forpeeling.

Barrier Compositions

The identity and composition of barrier compositions that can beinterposed between polymer sheets used in the articles and methods asdescribed herein are not critical. A skilled artisan will recognize thatsubstantially any material can be used as a barrier composition betweentwo polymers, so long as it substantially prevents fusion of twopolymers under conditions at which at least one of the polymers can bethermoformed. A wide variety of such compositions are known for thispurpose. Barrier compositions used to make shaped articles for food usesshould, of course, be selected for compatibility with foodstuffs.

Examples of suitable barrier compositions include adhesives (e.g.,peelable adhesives such as pressure-sensitive adhesives), known polymerrelease agents, a polymeric or paper film interposed between polymerlayers, and various liquids, including low-viscosity silicone oils.

A composition interposed between two surfaces (e.g., between the firstand second polymer sheets, or between two second polymer sheets, asdescribed herein) can act as a barrier composition between the twosurfaces if the composition coats at least one of the two surfaces at athermoforming condition, thereby preventing surface-to-surface contactand fusion of the two surfaces at the thermoforming condition.

A barrier composition prevents fusion of opposed polymeric surfaces onlywhen it is interposed between the surfaces at the thermoformingcondition. For that reason, the barrier composition must be interposedbetween the surfaces over the entire area for which fusion between thesurfaces is not desired. This can be achieved in various ways, includinguse of liquid and solid barrier compositions. When a stack is to bethermoformed to make a plurality of shaped objects that are not fusedover some portions, but fused at at least one portion (e.g., a stack ofmeat trays fused only at a single, frangible extension of the trays atone corner), the barrier composition is interposed among the polymersheets in the non-fused areas, but is not interposed between the polymersheets in the area in which fusion is desired.

Liquid barrier compositions should be selected such that they completelycoat (i.e., wet) at least one of the surfaces over the entire area forwhich fusion is not desired. This can be achieved by selecting a liquidbarrier composition (i.e., a composition that is a liquid at at leastthe thermoforming condition, regardless of whether it is a liquid atwhich it is contacted with the surface) that has a surface tensionsignificantly greater (i.e., at least 2 Dynes per centimeter, andpreferably at least 10 Dynes per centimeter greater) than the surfaceenergy of the surface with which it is contacted. This surface energydifference should ensure that the liquid barrier composition completelywets (i.e., coats) the area of the surface for which fusion is notdesired. Preferably, the liquid barrier composition has a surfacetension significantly greater than the surface energy of both surfaces,so that the liquid is not displaced from between the surfaces at pointsat which the two surfaces are urged tightly against one another.

Solid barrier compositions (e.g., polymer sheets) should be selected sothat the solid covers the entire area for which fusion is not desired.The identity of the solid is not critical, so long as it does notprevent the portions of a polymer sheet that are to be thermoformed fromreaching the thermoforming condition. Solid barrier compositions canprevent fusion of the surfaces (and/or) fail to fuse to one or bothsurfaces for a variety of reasons, any of which are sufficient to rendera material suitable as a solid barrier composition. Some solids can bepredicted to act as suitable barrier compositions, while other mayrequire empirical testing (e.g., thermoforming two sheets of the polymerwith the solid interposed between them) in order to determine theirsuitability. Either way, selection of an appropriate solid barriercomposition is within the ken of a skilled artisan in this field.

Another type of barrier composition that can be used is a compositionincorporated as an additive into one or both of the polymer sheets.These compositions melt and “bloom” to the surface of a polymer whenheated, pressed, stretched, or otherwise manipulated. If such acomposition is included in one or both of the polymer sheets such thatthe composition blooms at the surface of at least one sheet at thethermoforming condition and prevents contact between the polymer sheetsthemselves, then the composition can be used as a barrier composition inthe articles and methods described herein. A wide variety ofcompositions that exhibit such blooming behavior are known in the art.

Adhesives

The identity and composition of adhesive that can be interposed betweenpolymer sheets used in the articles and methods as described herein arenot critical. A skilled artisan will recognize that substantially anymaterial can be used as an adhesive between two polymers, so long as itreversibly binds the two polymer layers and requires no more force toseparate the polymer layers than can be practically applied to thepolymer layers by a person of ordinary strength. A wide variety of suchcompositions are known for this purpose. For food-contacting articlesdescribed herein, any adhesive employed should be selected forcompatibility with foodstuffs.

When an adhesive is used between two polymer sheets, it can be used tocoat substantially the entire interfacial region between the two sheets(to “flood coat” them). Adhesive can be excluded from a portion of theinterfacial region, to permit fusion (if no other barrier composition ispresent) or to leave a non-adhered portion to facilitate peeling.

The adhesives used between a peelable polymer sheet and an underlyingsurface are preferably peelable, meaning that the polymer sheet can bepeeled from the surface by a person of ordinary strength, preferablywithout tearing or substantially stretching the sheet. Preferably, anadhesive having a coat weight of roughly 0.6 to 15 ounces per inch isused to adhere a peelable sheet to an underlying surface.

A wide variety of suitable adhesives are known in the art and can beused as described herein. Pressure-sensitive adhesives are among thesuitable adhesives that can be used. Likewise, adhesives that adherepreferentially to one of two adhered surfaces, upon peeling of one ofthe surfaces away from the other) are suitable and are preferred incertain embodiments. By way of example, if an adhesive adheres morestrongly to a peelable polymer sheet than to a surface to which thesheet is adhered by the adhesive, the adhesive will tend to remain withthe sheet when it is peeled from the surface.

Various compounds and surface treatments can be used to reduce the forceneeded to pull an adhesive from a surface, and such compounds andtreatments can be used to modulate adhesion of an adhesive to a surfacedescribed herein.

Specific examples of adhesives that can be used in the articlesdescribed herein include polysiloxane-based adhesives, rubber cement,and acrylic adhesives (e.g., waterborne pressure-sensitive, acrylicadhesives of the MULTI-LOK brand family of acrylic adhesivesmanufactured by National Adhesives of Bridgewater, N.J.).

Thermoforming Apparatus and Conditions

The articles described herein can be made using known thermoformingapparatus and conditions. Of course, the apparatus and conditions shouldbe selected based on the identity and the characteristics of thematerials to be processed. Selection of appropriate thermoformingconditions, based on the identity(ies) of the materials to be processedis within the ken of a skilled artisan in this field.

Printing

Text, images, or other graphical material can be printed onto one ormore faces of one or more of the polymer sheets described herein. A widevariety of materials and methods can be used to print such material ontothe surface of a polymer sheet. A difficulty inherent in printing onpolymer materials is that the printed matter can often easily bedisplaced from the polymer surface by heat, light, or mechanicalabrasion, leading to reduced print quality. Furthermore, it can beundesirable for the materials used for printing to contact materialswithin the compartment.

The tenacity of binding of printed matter to a polymer sheet can, asdescribed herein for adhesives, be affected by surface treatment of thepolymer sheet prior to printing upon it. Corona treatment and plasmadischarge techniques, for example, can raise the surface energy of apolymer surface, rendering it susceptible to more tenacious binding bythe printed matter. Likewise, surface treatment (e.g., Corona treatment)of a polymer surface having printed matter thereon can raise the surfaceenergy of the surface (including the portion on which the printed matterappears). It can be preferably to enhance or reduce the surface energyof the surface of one of two polymer sheets that are adhered or adhesedin an article described herein, so that when the two sheets areseparated from one another, most or all of the printed matter at theinterface of the two sheets will remain attached to one of the twosheets.

Inks, binders, materials used to prepare a surface to receive printing,and products formed by surface preparation can include products whichare undesirable in food products. Thus, when articles described hereinare to be used both to carry printing and to contain or contact foodproducts, care should be taken either to select printing and surfacepreparation materials appropriate for use for food containers (i.e.,safe for consumption or insoluble in food) or to create a barrierbetween food and any such materials (i.e., to prevent their migrationinto food).

By way of example, in a food container consisting of a thickthermoformable substrate having a thin, pliable liner sheet peelablyadhered thereto, substantially any material that does not migrate underordinary food packing and storage conditions through the liner sheet canbe used for printing upon the substrate or for preparing the surface ofthe substrate for printing. At least in portions of the container inwhich the liner is interposed between the substrate and food stored inthe container, the presence of the liner will inhibit or preventsubstantial migration of such components from the surface of thesubstrate into the food. Thus, even an ink which is inappropriate forinclusion in a food and which would normally dissolve in the food can beused to print upon the substrate of the food container, so long as aliner sheet through which the ink cannot migrate under ordinaryconditions is interposed between the food in the container and thesurface to which the ink is applied (regardless of whether othermaterials are interposed between the ink and the food). If thecharacters or images printed on the substrate are to be viewed throughthe liner, then the liner should be sufficiently transparent ortranslucent that such viewing is possible.

One embodiment (referred to as “two-side printed containers”) of a foodcontainer described herein is a generally planar tray or dish that bearsprinting that is visible from both faces of the container and issuitable for containing a food even if a material used in the printingprocess is unsuitable for contacting with the food. This embodimentincludes both a substrate sheet (e.g., a relatively thick thermoformablematerial such as virgin PET or RPET) and a relatively thin liner sheet(e.g., a clear monolithic PE sheet or a clear or translucent multi-layersheet in which a layer of EVOH is sandwiched between PE layers).Interposed between the substrate sheet and the liner sheet is agenerally opaque printed sheet that bears characters, diagrams, images,or other visual indicia on one or both faces thereof.

In two-side printed containers, the identity of the printed sheet is notcritical, other than that it should be fixably emplaceable between theliner and substrate sheets (i.e., fusible with, adherable to, oradhesible to both the substrate sheet and the liner sheet orsufficiently perforated that binding between the substrate and linersheets is sufficient to hold the printed sheet in place withoutcompromising the structural integrity of the finished container). In itsassembled state, a two-side printed container has the liner sheet on itsfood-bearing face(s), the liner sheet overlying the printed sheet (suchthat indicia on the printed sheet are preferably visible through theliner sheet), and the printed sheet overlying the substrate sheet (suchthat indicia on the printed sheet are preferably visible through thesubstrate). In this assembled state, the substrate can provide bulkphysical properties (e.g., rigidity and shape), the printed sheet canprovide a desired visual appearance, and the liner sheet can preventtransfer of any undesirable materials present on or in the printed sheetor substrate sheet into the food that contacts the liner on the face ofthe liner opposite the face opposed against the printed sheet andsubstrate sheet.

As with other lined containers described herein, two-side printedcontainers can be combined with a lidstock material that closes one ormore orifices of or spaces in the container. The lidstock can bepeelably adhered or adhesed to one or more portions of the container,fused with one or more portions of the container, or a combination ofthese. For food storage applications, a food-compatible lidstock ispreferably sealed about the perimeter of an area or cavity defined by afood-compatible liner material, which can be peelably or tenaciouslyattached to a substrate material. By way of example, a lidstock materialhaving a face made from the same material (e.g., ULDPE) as the face of aliner sheet can be fused with the liner sheet when the two faces areopposed against one another at a temperature sufficient to melt thematerial. The lidstock can have printed matter thereon, the printingoccurring before application of the lidstock to the container (e.g.,application of a pre-printed package design), after such application andsealing of the container (e.g., application of a “packed on” or “use by”date), or a combination of these. Decals, stickers, price tags, papersleeves, and other known product package components can also be addedduring or after packaging.

In a specialized embodiment of two-side printed containers, each of theliner sheet and the substrate sheet is substantially clear and theprinted sheet is both substantially opaque and printed on both facesthereof. In addition, one face of the printed sheet has a material onits surface that bonds to the liner sheet more tenaciously than theprinted sheet binds to the substrate in the finished container (i.e., sothat the liner and printed sheets can be peeled together from thesubstrate sheet). By way of example, the face of the printed sheetopposed against a liner sheet can be made of the same material as theopposed face of the liner sheet (e.g., each face can be the same PE),such that the two sheets fuse upon thermoforming or upon passage througha hot-nip roller that transmits sufficient heat to melt the opposedfaces. Alternatively, a unitary container can be made by thermoforming aliner sheet, a printed sheet, and a substrate sheet wherein the opposedfaces of the liner and printed sheets are made from the same materialand the opposed faces of the printed and substrate sheets are also madefrom the same material (not necessarily the same as the opposed faces ofthe liner and printed sheet faces), such that when the three sheets arethermoformed, the liner sheet fuses with the printed sheet, the printedsheet fuses with the substrate sheet, and a unitary container results.

In two-side printed containers, printing on the face of the printedsheet facing the liner sheet can include, for example, recyclinginstructions, instructions for removing the printed and liner sheetsfrom the substrate sheet, instructions or a diagram for positioning foodto be contained on the container prior to sealing, recipes or cookinginstructions for the food to be contained, and the like. Printing of theface of the printed sheet facing the substrate sheet can include, forexample, nutritional information, contact information for the foodmanufacturer or packager, recipes or cooking instructions for the foodto be contained, instructions for disassembling the container andrecycling one or more parts thereof, trade marks or trade dressmaterial, and design or graphical materials.

Meat Trays and Other Shaped Articles

In one embodiment, the subject matter disclosed herein includes a meattray including at least a substrate sheet and a liner sheet that aresimultaneously thermoformed to form the tray. As used herein, the term“thermoformed” is intended to encompass various methods of shaping athermoplastic sheet or stacked sheets by heating the sheet and applyinga pressure differential to the opposed side of the sheet to conform thesheet to the shape of a mold surface.

While the subject matter of this disclosure is occasionally described interms of the preferred embodiment of simultaneously thermoformingsubstrate and liner sheets, it will be understood after reading thedisclosure that the subject matter also includes simultaneously forminga substrate and a single liner sheet, and shaping the liner sheets andsubstrate by other means, e.g., by stamping, injection molding or blowmolding. The substrate sheet, while preferably a thermoformable plastic,may also be of other materials, e.g., metals.

In one example of thermoforming known as vacuum molding, a sheet ispositioned adjacent a female (or, less commonly, male) mold section anda vacuum is applied to draw the sheet against the mold surface. A malemold section may be pressed against the sheet on the opposite side ofthe sheet from the female mold section to assist in conforming the sheetto the shape of the female mold section. However, when a male mold isused to assist in forming shaped articles described herein, care must betaken that the male mold does not prevent separation between thesubstrate and liner sheets and consequent reservoir formation.

In a preferred embodiment of the subject matter disclosed herein, astack comprising a planar sheet of thin (e.g., 1-7 mil) plastic (“linersheet”) is positioned on a surface of a planar substrate sheet of agreater thickness (e.g., 10-40 mils) to be formed into a meat tray. Anadditional liner/substrate sheet stack may be layered atop the firststack if a barrier composition is interposed between the stack toprevent their fusion.

The sheets can be provided in either sheet form or roll form. Forconvenience in shipping, storage, and thermoforming, the stacked sheetsmay be provided to the thermoformer in a continuous roll form, with abarrier composition interposed between the layers of the roll. The rollcan be continuously fed through the thermoformer, with each length oftray sheet being indexed, then thermoformed into a shape, i.e., a meattray. The roll length and width can be as desired. For example, themaster pad roll can be 5″ to 60″ in width.

The stack of sheets is thermoformed as a unit into the shape of thedesired article, e.g., a meat tray having the liner sheet on the concaveinterior of the meat tray. Upon cooling, the tray maintains itsthermoformed configuration due to the thickness and rigidity of thesubstrate sheet; the configuration of the liner sheets can be set bythermoforming or assisted by the presence of an inter-sheet adhesive.

The meat tray is used like a traditional one would use an ordinary meattray that does not have a liner. However, unlike prior art meat traysdescribed above, there is no need to place a ‘diaper’ or other absorbentliner into the tray or attempt. After use, the upper liner sheet can besimply peeled away to release exudate sequestered within thereservoir(s) between the substrate and liner sheets or between adheredmultiple liner sheets.

The mold, and thereby the thermoformed tray system, can be of variousshapes. Generally, the resultant tray will have an open-top interiorcavity with a floor and continuous side walls. The shaped article mayinclude ridged, flat, or other shaped portions, as with traditional meattrays and other food containers. The shaped article may also haveseparate sections for containing discrete food portions section, andeach compartment may have one or more reservoirs that communicate withthe interior of the compartment or with reservoirs of othercompartments, as desired.

Use of the Container

The container described herein can be used to isolate articles containedwithin the compartment. An important intended use of containersdescribed herein (especially layered reservoir containers) is to containfood products, such as cuts of meat, poultry, or seafood, that have atendency to release liquid (to “weep,” the liquid sometimes beingreferred to as “purge”) or otherwise soil their containers, such thatthe soiled container is ordinarily rendered unsuitable for recycling.

Containers for weeping food products frequently contain an absorbentmaterial for absorbing the purge. Even when an absorbent material ispresent, the container can become soiled and contaminated to a degreethat consumers do not wish to recycle it, and many municipalitiesprohibit inclusion of such items in recycling streams. Even if theabsorbent material is not attached to the container, the foulness of theabsorbent material can lead consumers to discard the entire container,rather than attempting to sort and clean its various parts, particularlyin view of the messiness that such cleaning entails. Food packagingwastes constitute a substantial portion of current solid waste streamssent to landfills.

Weeping food products contained within the containers described hereinweep just as in previously known containers. However, once the foodproduct is removed from them, the lidding and liner can be peeled fromthe substrate and discarded, yielding a substantially clean substratethat is suitable for inclusion in recycling streams. By recycling thesubstrate and discarding only the relatively thin liner and liddinglayers, the volume and weight of materials sent to landfills can besubstantially reduced. Furthermore, consumers increasingly seek productshaving a minimum of non-recyclable packaging.

The food container described herein is typically used by pre-formingsubstrates having the liner sheet peelably adhered to a face thereof.Preferably the substrate has a conformation that includes a concaveportion (e.g., a bowl, or a high-walled tray) for containing a fooditem. The liner covers the concave portion. After the food item isplaced onto or within the substrate, a lidding material is attached tothe liner material to form a closed compartment (e.g., by bonding orfusing the lidding and liner around the edges of the bowl or walls ofthe substrate) that encloses the food item.

A variety of liner and lidding items have been used in prototypecontainers having a substrate formed from amorphous PET or PETG.Suitable materials that have been identified include at least thefollowing laminated polymer sheets:

a multi-layer sheet consisting of LLDPE—tie layer—EVOH—tie layer—LLDPE;

a multi-layer sheet consisting of (a mixture of ULDPE and LLDPE)—tielayer—EVOH—tie layer—LLDPE;

a multi-layer sheet consisting of LLDPE—tie layer—EVOH—tie layer—PETG;

a multi-layer sheet consisting of (a mixture of ULDPE and LLDPE)—tielayer—EVOH—tie layer—PETG; and

ICE (TM; Bemis Europe, Soignies Belgium) brand high performance barrierfilm.

The disclosure of every patent, patent application, and publicationcited herein is hereby incorporated herein by reference in its entirety.

While this subject matter has been disclosed with reference to specificembodiments, it is apparent that other embodiments and variations can bedevised by others skilled in the art without departing from the truespirit and scope of the subject matter described herein. The appendedclaims include all such embodiments and equivalent variations.

1. A shaped article comprising: a) a thermoplastic sheet having a shapewhich includes a concave interior portion and a peripheral edge, thethermoplastic sheet including an extension and a bent portion, theextension extending peripherally away from the interior portion andincluding the peripheral edge, and the bent portion being interposedbetween the peripheral edge and the junction between the body and theextension, the bent portion having a smooth periphery and beingsufficiently bent that the peripheral edge is displaced from theperiphery of the article, whereby the article has a smooth periphery;and b) at least one pliable liner sheet conforming to and being peelablyattached to the thermoplastic sheet.
 2. The shaped article of claim 1,wherein at least one liner sheet is peelable attached to each of theinterior portion, the extension, and the bent portion of thethermoplastic sheet.
 3. The shaped article of claim 1, wherein each ofthe peripheral edge, the bent portion, and the extension completelysurrounds the interior portion, and wherein each of the interiorportion, the extension, and the bent portion of the thermoplastic sheethas a liner sheet peelably attached thereto.
 4. The shaped article ofclaim 3, wherein the same liner sheet is peelably attached to each ofthe interior portion, the extension, and the bent portion of thethermoplastic sheet.
 5. The shaped article of claim 4, wherein the linersheet is delaminated from the thermoplastic sheet at at least a portionof the peripheral edge.
 6. The shaped article of claim 4, wherein agraspable tab is interposed between the liner sheet and thethermoplastic sheet at at least one position along the peripheral edge.7. The shaped article of claim 4, further comprising a lidding attachedto the liner sheet completely around the interior portion.
 8. The shapedarticle of claim 7, wherein the lidding is attached to the liner by wayof a gas-tight seal and the space between the lidding and the liner withthe seal contains a gas.
 9. The shaped article of claim 7, wherein thelidding is attached to the liner by way of a gas-tight seal and whereinthe lidding and the liner contain between them at least one item notincluding any substantial amount of a gas.
 10. The shaped article ofclaim 1, wherein the thermoplastic sheet includes a reservoir portionrecessed away from and entirely within the interior portion and whereinat least the liner sheet that is peelably attached most distally fromthe thermoplastic sheet surface bears a perforation therethrough at thereservoir portion, does not conform to the thermoplastic sheet at thereservoir portion, and is not peelably attached to the thermoplasticsheet at the reservoir portion, whereby liquid in the lumen of theinterior portion is able to traverse the liner sheet at the reservoirportion.
 11. The shaped article of claim 10, comprising i) anon-perforated liner sheet which is peelably attached to thethermoplastic sheet at each of the reservoir portion, the interiorportion, the extension, and the bent portion of the thermoplastic sheetand ii) the perforated liner sheet attached to the non-perforated linersheet.
 12. The shaped article of claim 1, wherein the extension includesthe peripheral edge, a flat sealing surface surrounding the concaveinterior portion, and the bent portion interposed between the peripheraledge and the sealing surface, the sealing surface being suitable forsealing the sealing film thereto using either of VSP and MAP sealingtechnologies, and the bent portion being bent sufficiently that theperipheral edge is turned at least approximately opposite the periphery.13. The shaped article of claim 1, wherein the peripheral edge is turnedaway from the periphery of the tray.
 14. The shaped article of claim 1,having the overall shape of a rectangular tray with rounded corners. 15.The shaped article of claim 1, wherein the bent portion includes arounded portion.
 16. The shaped article of claim 15, wherein the roundedportion has a J-shaped conformation.
 17. The shaped article of claim 15,wherein the rounded portion has a U-shaped conformation.
 18. The shapedarticle of claim 15, wherein the rounded portion has a spiralconformation.
 19. The shaped article of claim 1, wherein the extensionbears a flat sealing surface and completely surrounds the concaveinterior portion of the body.
 20. The shaped article of claim 19,wherein a gap exists between the bent portion and the concave interiorportion of the body.
 21. The tray of claim 20, wherein the gap occursabout the entire periphery of the article.
 22. The tray of claim 21,wherein the width of the gap at each position about the concave interiorportion of the body is at least half the width, measured in thedirection extending peripherally away from the concave portion of thebody, of the flat sealing surface at that position.
 23. The tray ofclaim 21, wherein the width of the gap at each position about theconcave interior portion of the body being at least three-quarters thewidth, measured in the direction extending peripherally away from theconcave portion of the body, of the sealing surface at that position.24. A shaped article comprising: a) a thermoplastic sheet having a shapewhich includes a concave interior portion and a peripheral edge, thethermoplastic sheet including a spacer bearing a peripheral edge, thespacer being connected to the body by way of an extension that extendsperipherally away from the body and a bend region interconnecting thespacer and the extension, the bend region having a smooth contour andinterconnecting the spacer at an approximately right angle with theextension b) at least one liner sheet conforming to and being laminatedagainst the thermoplastic sheet.
 25. The shaped article of claim 24,wherein at least one liner sheet is peelable attached to each of theinterior portion, the extension, and the bent portion of the substratesheet.
 26. The shaped article of claim 24, wherein the liner sheet isperforated.
 27. An article comprising a thermoplastic sheet having aperipheral edge and defining a shaped body having an extension extendingperipherally away from the body, the extension including the peripheraledge, and a bent portion interposed between the peripheral edge and thejunction between the body and the extension, the bent portion having asmooth periphery and being sufficiently bent that the peripheral edge ofthe thermoplastic sheet is displaced from the periphery of the article,yielding an article having a smooth periphery; and a pliable linerpeelably attached to the thermoplastic sheet.
 28. The article of claim27, including multiple pliable liners peelably attached to thethermoplastic sheet.
 29. The article of claim 27, wherein the liner isdelaminated from the thermoplastic sheet at at least a portion of theperipheral edge.
 30. The article of claim 27, wherein the peelable layeris a non-thermoplastic material. 31-53. (canceled)